Low carbon footprint magnesia production

Abstract

To provide a method for producing magnesia that reduces CO2 emissions from decarbonization during magnesia production through recycling and improves energy efficiency. [Solution] A method for producing magnesia includes subjecting a magnesium-containing material to carbonation, which includes contacting a CO2-containing gas with the magnesium-containing material; and calcining the magnesium carbonate to produce a CO2 by-product and magnesia; and wherein subjecting the magnesium-containing material to carbonation further includes: recycling at least a portion of the CO2 by-product as a recycled CO2 by-product, and contacting the magnesium-containing material with the recycled CO2 by-product; and controlling the relative amount of the recycled CO2 by-product to the CO2-containing gas to obtain a constant CO2 content supplied to the carbonation.

Description

[Technical field]

[0001] The technical field relates generally to the production of magnesia from magnesium carbonate, and more particularly to the integration of magnesia production with carbon dioxide sequestration and the use of magnesium-bearing ultramafic rocks such as serpentinite. [Background technology]

[0002] Magnesia (MgO) is the most common primary material used in the refractory industry. It is conventionally produced by calcination of magnesite (MgCO3), which is derived from natural deposits, or by precipitation from brines. Summary of the Invention [Problem to be solved by the invention]

[0003] The calcination route poses various environmental challenges but has been the most used to date. The CO2 emissions and associated energy requirements from the decarbonization that occurs during magnesia production are problematic.

[0004] Energy efficiency and the use of alternative energy sources can reduce CO2 emissions, but more than 50% of process emissions come from the process itself.

[0005] Natural magnesite deposits around the Earth are large natural reservoirs of CO2 that are permanently captured and safely stored, based on natural geological processes occurring over thousands of years.

[0006] Unfortunately, such materials are also the major source of MgO production used in various industries, resulting in this CO2 being returned to the atmosphere and therefore contributing to global warming.

[0007] What is needed is a technique that overcomes at least some of the shortcomings of known methods for producing magnesia. [Means for solving the problem]

[0008] In some embodiments, a method for producing magnesia is provided that includes contacting a C02-containing effluent with a magnesium-containing material to produce magnesium carbonate; calcining the magnesium carbonate to produce a C02 by-product and magnesia, and recycling at least a portion of the C02 by-product to contact the magnesium-containing material to produce magnesium carbonate.

[0009] In some embodiments, the contacting step further comprises providing the magnesium-containing material in an aqueous slurry and contacting the CO2-containing effluent and the CO2 by-product with the aqueous slurry.

[0010] In some embodiments, the method includes the steps of producing a carbonate loaded slurry comprising precipitable carbonate and substantially free of precipitated alkaline earth metal carbonate in the contacting step, separating the carbonate loaded slurry into an aqueous phase comprising precipitable carbonate and a solid phase, precipitating magnesium carbonate from the aqueous phase, and separating the magnesium carbonate from the aqueous phase.

[0011] In some embodiments, the CO2-containing effluent comprises combustion gases from a magnesia manufacturing facility.

[0012] In some embodiments, the combustion gases are derived from a calcination step. The combustion gases may be derived from a thermal activation step of the magnesium-containing material prior to contact with the CO2-containing effluent.

[0013] In some embodiments, the CO2 used to contact the magnesium-containing material is obtained exclusively from a magnesia production facility.

[0014] In some embodiments, the CO2-containing emissions include emissions from separate sources.

[0015] In some embodiments, the method includes subjecting the magnesium-containing material to a thermal activation pretreatment prior to contacting with the CO2-containing effluent. In some embodiments, the thermal activation pretreatment is carried out at a temperature of about 600-700°C.

[0016] In some embodiments, the heat activated pretreatment is carried out for a duration of about 20 to 60 minutes.

[0017] In some embodiments, CO2 from a thermal activation pretreatment is fed to the contacting step.

[0018] In some embodiments, the magnesium-containing material is contacted with a CO2 feed stream that comprises a plurality of CO2 source streams.

[0019] The method may also include controlling the relative amount of each CO2 source stream in the CO2 feed stream.

[0020] Control can occur according to the pressure, temperature and / or composition of the CO2 source stream.

[0021] In some embodiments, the CO2 feed stream further comprises CO2 derived from an additional magnesia production train.

[0022] In some embodiments, the additional magnesia production train comprises a conventional production train.

[0023] In some embodiments, the magnesium-containing material comprises serpentine or is derived from serpentine or a variant thereof.

[0024] In some embodiments, the magnesium-containing material is derived from a naturally occurring mineral material.

[0025] In some embodiments, the magnesium-containing material is derived from at least one of basalt, peridotite, serpentine, ophiolitic rock, mafic rock, ultramafic rocks, peridot, pyroxene, olivine, serpentinized peridotite, magnesium oxide-containing minerals, and / or brucite.

[0026] In some embodiments, the magnesium-containing material is pre-treated prior to carbonation to produce a magnesium-containing particulate material having a magnesium content of about 1% to about 35% by weight.

[0027] In some embodiments, the magnesium content is from about 10% to about 30% by weight.

[0028] In some embodiments, the magnesium-containing material is derived from an industrial by-product material.

[0029] The industrial by-product materials may include steelmaking slag and / or steelmaking worn magnesium oxide bricks.

[0030] In some embodiments, the magnesium-containing material is derived from a mineral residue.

[0031] The mining residues may include phyllosilicate mining residues and / or white asbestos mining residues.

[0032] In some embodiments, the contacting step includes contacting the CO in a substantially dry form with the magnesium-containing material in at least one carbonation unit at a carbonation temperature of about 200 degrees to about 500 degrees Celsius and a carbonation pressure of about 1 bar to about 20 bar to carbonate the carbon dioxide gas to produce magnesium carbonate and a CO2-depleted gas.

[0033] In some embodiments, the method includes subjecting the magnesium-containing material to size reduction and removing the magnetic fraction prior to carbonation.

[0034] In some embodiments, the method includes milling the starting material to provide a particle size between about 200 microns and about 1000 microns to produce a sized material, removing the magnetic fraction from the sized material to produce a non-magnetic fraction, and milling the non-magnetic fraction to produce a magnesium-containing material having a particle size of up to 75 microns.

[0035] In some embodiments, the firing is carried out in an indirectly heated firing unit. Firing can be carried out in a direct heat firing unit.

[0036] In some embodiments, the process includes controlling at least one property of the CO2-containing gas that contacts the magnesium-containing material.

[0037] The control may include adjusting the relative amounts of the CO2-containing effluent, and the CO2 by-product is used to contact the magnesium-containing material.

[0038] Control may be performed to control the gas pressure, gas temperature, and / or CO2 content of the CO2-containing gas in contact with the magnesium-containing material.

[0039] In some embodiments, the process includes one or more features of the magnesium carbonate production methods described herein.

[0040] In some embodiments, a method for producing magnesia is provided: The CO2-containing gas is contacted with a magnesium-containing material to produce magnesium carbonate; the magnesium carbonate is calcined to produce a CO2 by-product and magnesia; and at least a portion of the CO2 by-product is recycled as at least a portion of the CO2-containing gas for contacting the magnesium-containing material to produce magnesium carbonate.

[0041] Such a process may include one or more features described above or herein.

[0042] In some embodiments, a method for producing magnesia is provided: The CO2-containing gas is contacted with a magnesium-containing material in an aqueous slurry, precipitated magnesium carbonate is recovered from the aqueous slurry, and the precipitated magnesium carbonate is calcined to produce a CO2 by-product and magnesia.

[0043] Such a process may include one or more features described above or herein.

[0044] In some embodiments, the magnesium carbonate comprises or consists of nesquehonite.

[0045] In some embodiments, a magnesia production system is provided that includes: At least one carbonation unit: a gas inlet for receiving a CO2-containing gas; a slurry inlet for receiving an aqueous slurry including the magnesium-containing material; a carbonation vessel for carbonate at least a portion of the magnesium in the aqueous slurry with CO2 to produce a CO2-depleted gas; and a carbonate loaded slurry comprising precipitateable magnesium carbonate; a slurry outlet for discharging a carbonate loaded slurry comprising the precipitateable magnesium carbonate; and Gas outlet for releasing CO2 exhausted gas; Separation Unit: a slurry inlet for receiving a carbonate load slurry comprising precipitateable magnesium carbonate from a slurry outlet of the at least one carbonation unit; a separation chamber for separating the carbonate-laden slurry containing the precipitated magnesium carbonate into a solid phase and an aqueous phase containing the precipitated magnesium carbonate; a liquid outlet for discharging the aqueous phase; and A precipitation unit having: a slurry inlet for receiving an aqueous phase comprising precipitable magnesium carbonate from the liquid outlet of the separation unit; a precipitation chamber for precipitating the magnesium carbonate and forming a precipitate slurry; and A liquid outlet for discharging the settling slurry; a calcination unit that receives at least a portion of the magnesium carbonate and produces a calcined magnesia material and a CO2 by-product stream.

[0046] In some embodiments, the system includes a CO2 collection and delivery system that collects the CO2 by-product stream as at least a portion of the CO2-containing gas and delivers the CO2 by-product stream to the carbonation unit.

[0047] In some embodiments, the system includes any one of claims 1-39 or at least one additional feature described or exemplified herein.

[0048] In some embodiments, there is provided the use of phyllosilicate mine residues to sequester carbon dioxide from industrial emissions and produce magnesia.

[0049] In some embodiments, there is provided the use of precipitated magnesium carbonate derived from the sequestration of CO2 emissions by magnesium-containing materials for the production of magnesia by calcination.

[0050] In some embodiments, there is provided the use of precipitated nesquehonite for the production of magnesia by calcination.

[0051] In some embodiments, a method of producing magnesia includes providing magnesium carbonate comprising precipitated nesquehonite to a calcination unit and calcining the precipitated nesquehonite to produce magnesia.

[0052] In some embodiments, there is provided a magnesia product produced by calcination of precipitated magnesium carbonate derived by contacting a magnesium-containing material in wet or dry form with carbon dioxide from an industrial effluent in a carbonation unit to form a carbonate-loaded slurry, and precipitating calcium or magnesium carbonate from the carbonate-loaded slurry in a precipitation unit.

[0053] In some embodiments, the precipitated magnesium carbonate comprises nesquehonite.

[0054] In some embodiments, the process includes recovering a C02-containing by-product stream from the calcination and subjecting the C02-containing by-product to water removal to produce a treated C02 by-product stream prior to contacting the treated C02 by-product stream with the magnesium-containing material.

[0055] In some embodiments, the magnesium-containing material comprises an evaporite. In some embodiments, the evaporite is derived from an evaporator unit. In some embodiments, the evaporite comprises magnesium chloride salts. In some embodiments, the evaporite comprises magnesium sulfide salts. In some embodiments, the evaporite comprises magnesium carbonate salts. In some embodiments, the evaporite is pretreated prior to carbonation.

[0056] It should be noted that one or more of the features described above or herein may be combined in a process, system, use, and / or product as described above or herein.

[0057] Several embodiments, aspects, and implementations of the present technology are illustrated in and may be further understood in conjunction with the following drawings. Effect of the Invention

[0058] To overcome at least some of the shortcomings of known methods for producing magnesia. [Brief description of the drawings]

[0059] [Figure 1] FIG. 1 is a process flow diagram for wet carbonation. [Diagram 2] FIG. 2 is a schematic diagram of a carbonation unit. [Diagram 3] FIG. 3 is a process flow diagram for wet carbonation. [Figure 4] FIG. 4 is a schematic diagram of the process steps for wet carbonation with a recirculation scenario. [Diagram 5] FIG. 5 is a graph of the amount of solubilized magnesium versus temperature for wet carbonation at three different reaction times. [Figure 6] FIG. 6 is a graph of solubilized magnesium versus temperature for wet carbonation of aqueous slurries having three different pulp densities. [Figure 7] FIG. 7 is a graph of CO2 removal versus gas / liquid ratio (GLR) for wet carbonation of aqueous slurries of various pulp densities. [Figure 8] FIG. 8 is a graph of CO2 removal versus time for wet carbonation. [Figure 9] FIG. 9 is a graph of CO2 flow rate versus time for wet carbonation in continuous mode showing CO2 removal efficiency at 3.4 bar and 42 mL / min. [Figure 10] FIG. 10 is a response surface graph showing the interaction of temperature and pressure on CO2 removal rate in direct dry gas solid carbonation. [Figure 11] FIG. 11 is a graph of pressure versus time for a 10 minute gas / solid carbonation at 258° C. and 5.6 atmospheres. [Figure 12] FIG. 12 is a schematic diagram of a method for producing MgO. [Figure 13] FIG. 13 is a schematic diagram of a process for producing MgO and integrating CO2 emission capture from another industrial flue gas. [Figure 14] FIG. 14 is, for example, a process diagram illustrating a two-train MgO production operation applicable as a potential retrofit of an existing MgO production facility.

[0060] While the invention will be described in conjunction with exemplary embodiments, it will be understood that it is not intended to limit the scope of the invention to those embodiments.

[0061] On the contrary, it is intended to cover all alternatives, modifications, and equivalents, which may be included as defined by the scope of the appended claims. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0062] Detailed Description Described herein are various technologies relating to the production of magnesia and utilization of CO2 emissions and by-product streams.

[0063] In some embodiments, the present technology facilitates the production of low carbon dioxide magnesia from serpentine carbonation of magnesium-containing materials, such as those derived from serpentine.

[0064] Magnesia Production Overview 12 and 13, the overall process for converting serpentine to magnesia is shown. Other magnesium-containing materials can also be used.

[0065] Serpentine may be provided from waste or residues or extracted as an ore. Serpentinite carbonation may be carried out and may include one or more characteristics as further described below, resulting in a relatively high quality magnesium carbonate stream, some examples of which may be referred to herein as nesquehonite, for use in magnesia production processes. It is noted that various forms of magnesite derived from carbonation of serpentine or similar magnesium-containing materials may be used as magnesia production feedstocks, including hydrated forms of magnesite, such as zipingite (Mg5(CO3)4(OH)2·5H2O), hydromagnesite (Mg5(CO3)4(OH)2·4H2O), other hydrated forms of magnesium carbonate hydrates, and combinations thereof.

[0066] The nesquehonite or other magnesite material provided by the carbonation operation can be used as a feedstock for the production of magnesia by calcination, which results in the production of a CO by-product that can be used in whole or in part to produce additional magnesite (e.g., nesquehonite) and then magnesia.

[0067] The CO2 used in the carbonation step can be derived from a separate industrial process, from the magnesia production process as a CO2-containing exhaust (e.g., from the combustion of hydrocarbons), and / or from at least a portion of the CO2 by-product stream from the calcination step. The carbonation step can be performed at the magnesia production site, particularly if the CO2 used for carbonation is exclusively from the magnesia production site. Alternatively, the carbonation step can be performed off-site at an industrial emitter, particularly if the CO2 used for carbonation is from the emitter.

[0068] The magnesia end product can be varied depending on the desired properties and processing conditions, which can be obtained by adjusting firing parameters such as firing time and temperature.

[0069] With reference to FIG. 12, during step 1, the serpentine can be crushed and ground to reach a particle size of about 200 μm-1000 μm, 300-700 μm, 400-600 μm, or about 500 μm. The magnetic fraction can then be removed by physical processing. Various magnetic separation techniques can be used. The magnetic fraction consists mainly of hematite / magnetite / chromite and represents a value-added product that can be further processed and sold. The non-magnetic fraction can be subjected to further particle size reduction to obtain magnesium-containing granular material with a particle size of up to 75 μm, up to 50 μm, up to 40 μm, or up to 30 μm.

[0070] A second size reduction step augments the subsequent carbonation step. In step 2, the non-magnetic serpentine is thermally activated. Thermal activation can be carried out at temperatures of approximately 600-700 °C for approximately 20-60 minutes. CO2 emissions associated with thermal activation can be collected for use in step 3.

[0071] The thermally activated serpentine is then used as a feedstock for the carbonation step (step 3). Here, the thermally activated serpentine reacts with the CO2 stream, which in some scenarios may be the gas stream coming from both step 2 and step 4. The CO2 gas composition can vary, for example, from 5% to 30%. Depending on the stage of the process (e.g., start-up, steady-state, turn-down, etc.), the CO2 content in the gas fed to the carbonation unit may vary. For example, during start-up, the CO2 content may correspond to, for example, a combustion gas content of about 5%-7%, while during steady-state operation, the CO2 content may correspond to a mixture of CO2 gas sources including both combustion gas and recycled CO2 by-product gas, and thus may be higher, in the range of 25%-30%. It should also be noted that in some scenarios the CO2 gas content may be much higher, for example, in the range of 50%-100%, when relatively pure CO2 is used, which may be the case in certain scenarios discussed further below.

[0072] Still referring to step 3, the first by-product material of step 3 is an amorphous silicate phase that can be used as a filler material. The second product of step 3 is magnesium carbonate, which can be fed to subsequent processing.

[0073] In step 4, magnesium carbonate is calcined to produce magnesia. In some embodiments, all of the CO2 by-product emissions from the calcination are diverted to be fed to step 3.

[0074] With reference to FIG. 13, low CO2 magnesia production can be associated with an industrial on-site CO2 capture plant. In this case, a second carbonation site (step 5) is added to the aforementioned scenario. By following this approach, magnesia production can be increased and CO2 emissions from other industrial plants can be reduced. In some embodiments, this methodology facilitates the production of low carbon magnesia obtained from magnesium-containing materials such as serpentine (Mg3Si2O5(OH)4)-based rocks. CO2 is converted to carbonate when it reacts with magnesium contained within the mineral structure. Following recent research, a process using serpentine to treat industrial exhaust gases has been developed, facilitating the economic reduction of CO2 emissions as well as the production of very high purity nesquehonite.

[0075] Such nesquehonite can then be used as a feedstock for further processing to advantageously produce magnesia by calcination. Furthermore, both the carbonation of serpentine and the decarbonation of magnesite can be carried out at a single industrial site to offset the CO2 emissions generated from magnesite roasting.

[0076] The result is a magnesia manufacturing operation where CO2 is recirculated in a circular process and not released into the atmosphere, giving a low carbon footprint and a high purity magnesia product.

[0077] In one aspect, the technology described herein can facilitate the production of magnesia without high CO2 emissions into the atmosphere when natural magnesite deposits are used as a feedstock.

[0078] In another aspect, the technology described herein can facilitate the integration of CO2 emissions from magnesite calcination to produce more magnesia from serpentine carbonation.

[0079] In another embodiment, the technology described herein can facilitate the production of magnesia from magnesite produced by serpentine carbonation using industrial CO2 released from another industrial site.

[0080] With reference to FIG. 14, it is noted that a magnesia production facility can include two or more trains, each producing an MgO output stream.

[0081] In Figure 14 there are two trains, one of which is a conventional train that receives a supply of magnesite from natural deposits for calcination, and a second train that can be new or modified as shown to include serpentine or similar material as a feedstock for carbonation-precipitation, with the resulting MgCO3 being fed to calcination to produce serpentine-derived MgO. Note that various CO2 streams are produced in such a multi-train process, and one or more of the CO2 streams can be used in the carbonation step.

[0082] The CO2 stream may be collected by a CO2 collection system, which may include piping, a compressor (if necessary, depending on pressure conditions), a vessel, a valve, a condenser, a particle filter, a heat exchanger for heating or cooling the gas, and / or a control unit. Depending on the availability and characteristics (e.g., pressure, temperature, CO2 content) of different CO2-containing streams, the input of the CO2 feed to the capture system and the carbonation unit may be adjusted. The CO2 collection and supply system may also be a relatively simple assembly that fluidly connects the gas outlet of the calcination unit to the gas inlet of the carbonation unit. In some scenarios, the CO2-containing gas is supplied directly to the carbonation unit without substantial intervening units, and in such scenarios the operating conditions of the calcination unit and the carbonation unit may be provided to facilitate direct CO2 supply between the two units.

[0083] Additionally, if there is an excess of potential CO2, there may be a storage unit that holds the CO2 from one or more selected sources. The CO2 collection and delivery system may have a variety of configurations. In some scenarios, the CO2 collection and delivery system is airtight to inhibit CO2 leakage.

[0084] The CO2 collection and delivery system may include a collection line in fluid communication with the calcination unit and a CO2 delivery line in fluid communication with the carbonation unit. Additionally, there may be one or more compressors and / or heat exchangers as part of the CO2 collection and delivery system to provide CO2 to the carbonation unit at the desired temperature and pressure. In some embodiments, the calcination unit is either a direct-heated calcination unit or an indirect-heated calcination unit. In direct-heated calcination, the resulting CO2-containing by-product stream is a mixed gas stream that includes CO2 from both the decarbonation of magnesite and the combustion of fuel and other gas components.

[0085] The CO2 by-product stream from the direct heated calciner may have a higher CO2 content than the combustion effluent and therefore may be more advantageous than the CO2 effluent for feed to the carbonator.

[0086] In indirectly heated calcination, the CO2-containing by-product stream is primarily CO2 from the decarbonation of magnesite, and its high CO2 content up to 100% may be more advantageous to feed into the carbonation unit than other CO2 streams (e.g., CO2 exhaust, CO2-containing by-product stream from direct heated calcination from another train, etc.) to provide a larger driving force for the carbonation reaction and smaller equipment size (e.g., vessels, pipes, etc.).

[0087] Additionally, the CO2-containing stream used in the carbonation unit can be selected based on higher pressure to facilitate the carbonation reaction. The CO2 stream from the combustion emission source can have a relatively low pressure, while the CO2 stream from the calcination can have a higher pressure and therefore can be selectively used for the carbonation step. For example, as the process progresses from start-up to normal operation, an increasing amount of CO2 from the calcination can be used for carbonation.

[0088] In some embodiments, the magnesium carbonate feedstock provided to the calcination comprises nesquehonite obtained from the carbonate precipitation process described herein. By providing the nesquehonite to the calcination with a predetermined hydration state, improved control and handling during the calcination process can be achieved. For example, when nesquehonite is provided to the calcination, a predetermined heat may be present based on the known hydration state of the nesquehonite, whereas magnesium carbonate derived from natural deposits may contain a complex mixture of hydrated materials where the enthalpy of dehydration is difficult to consistently determine.

[0089] Optional technologies for the production of magnesium carbonate and CO2 sequestration for integration with magnesia production A variety of optional techniques can be used in conjunction with the magnesia production practices described above to sequester carbon dioxide and produce alkaline earth metal carbonates for use in making magnesia.

[0090] In one embodiment, a method is provided for chemically sequestrating carbon dioxide from a carbon dioxide-containing gas by producing an alkaline earth metal carbonate in combination with a MgO production process. The carbon dioxide-containing gas originates from an industrial emission and can have a range of carbon dioxide concentrations according to the industrial process from which the emission originates.

[0091] In some optional embodiments, there is provided a method for chemically sequestrating carbon dioxide from carbon dioxide-containing industrial effluents by carbonation using magnesium or calcium silicate, preferably magnesium silicate or other magnesium-containing material, to provide a magnesium source in combination with an MgO production process.

[0092] In some embodiments, a similar manufacturing process can be carried out to produce CaO by utilizing the chemical sequestration of carbon dioxide from industrial emissions containing carbon dioxide by carbonation of calcium-containing materials. Most of the work to this point has been done with gases containing 100% CO2, which means that carbon dioxide from the smokestacks of industrial facilities must first be concentrated using a separate technique before it can be processed using carbonation. This means a more expensive process.

[0093] In 2011, a carbon capture and sequestration (CCS) pilot plant opened at a coal-fired power station in the UK. Experts estimated that 16% to 40% of the energy produced could ultimately be used to capture and store carbon. This would equate to a $100 million generating power facility, costing between $16 million and $40 million.

[0094] Embodiments of the present invention may allow for increased economic viability by providing benefits or costs of between zero and 10% of the value of the energy produced.

[0095] In some optional embodiments, it may be advantageous for the carbon dioxide-containing gas to be a gaseous effluent that is used directly as it is produced from the plant. For example, a cement plant may use a gas that contains 18.2% CO2, 4.11% O2, and 77.69% N2.

[0096] Optionally, the carbon dioxide-containing gas derived from industrial emissions can have a carbon dioxide concentration of from about 1% to about 30%.

[0097] The present invention may also enable the production of valuable alkaline earth metal carbonates from alkaline earth metal-containing materials. It is understood that the alkaline earth metal-containing materials may be natural materials, including but not limited to alkaline earth metal-containing minerals and alkaline earth metal-containing rocks. For example, the alkaline earth metal-containing materials may include serpentine or serpentite.

[0098] In some cases, the alkaline earth metal-bearing material may include alkaline earth metal-bearing rocks such as sandstone, granite, anorthite, basalt, serpentinite, peridotite, serpentinized peridotite, ophiolitic rock, mafic rock, ultramafic rocks (containing Mg and Fe minerals), rocks containing more than 10% pyroxene and peridot, or combinations thereof.

[0099] Optionally, the alkaline earth metal-containing material may include a phyllosilicate. Further optionally, the alkaline earth metal-containing material can include alkaline earth metal-containing minerals such as calcium silicate, magnesium silicate, feldspar, plagioclase feldspar (andesine), peridot (olivine sand), pyroxene (enstatite olivine sand), olivine, serpentine (as in the mineral family containing antigorite, leucite, and richardite), wollastonite, calcium oxide (CaO), magnesium oxide or periclase (MgO), brucite (Mg(OH)2), mafic and ultramafic rocks (containing Mg and Fe), or combinations thereof.

[0100] In some embodiments, the magnesium-containing material used as a feedstock may include magnesium-containing evaporite. Evaporites are deposits of precipitated minerals formed by the evaporation of aqueous solutions. Evaporite materials may potentially include high magnesium concentrations. Evaporites may include magnesium-containing particulate matter that is in a relatively reactive state due in part to its small particle size. Evaporites may be obtained from evaporator units used in various industries. Alternatively, the evaporite may be obtained from natural rocks formed by the evaporation of a former ocean or saltwater lake.

[0101] The evaporate may contain magnesium in the form of various magnesium salts of chloride, sulfate and / or caboanthate, such as carnallite (KMgCl3·6H2O), kainite (KMg(SO4)Cl·3H2O), ketserite (MgSO4·H2O), langbeinite (K2Mg2(SO4)3), polyhalite (K2Ca2Mg(SO4)6·H2O) and magnesite (MgCO3).

[0102] Depending on the chemical nature and physical structure of the evaporite material, it may be pre-treated using thermal and / or chemical steps to form a pre-treated magnesium-containing material for use in the carbonation step.

[0103] Alkaline earth metal-containing materials can also be produced from various industrial wastes or residues, such as slag, cement waste, mining processing waste, and mineral processing waste, which are available without the need to extract them from geological formations.

[0104] Optionally, the slag may include steel slag, steel wear MgO bricks, or a combination thereof.

[0105] Optionally, the cement waste may include rotary kiln dust (CKD, LKD), waste cement, waste concrete, construction and demolition waste, concrete with aggregates, concrete bricks, concrete, red bricks, or combinations thereof.

[0106] Optionally, the mining and mineral processing wastes may include phyllosilicate mining residues, white asbestos mining residues, serpentine (as in the rock matrix containing the ore), or combinations thereof.

[0107] Referring to FIG. 1, in some embodiments, the method includes providing a carbon dioxide containing gas 2 and an aqueous slurry 4 comprising an alkaline earth metal containing material 6 and water 8 to a carbonation unit 10 .

[0108] The carbonation unit 10 may include a gas inlet 12 for receiving a carbon dioxide containing gas 2 and a slurry inlet 14 for receiving an aqueous slurry 4 .

[0109] The method then includes contacting the carbon dioxide containing gas 2 with the aqueous slurry 4 in a carbonation unit 10 to carbonate at least a portion of the alkaline earth metal.

[0110] A carbon dioxide depleted gas 16 and a carbonate partial charge slurry 18 containing precipitated carbonates are produced.

[0111] The method may also include the steps of removing carbon dioxide depleted gas 16 from carbonation unit 10 through gas outlet 17 and removing carbonate-laden slurry 18 through slurry outlet 19.

[0112] In some embodiments, the carbonate loaded slurry is substantially free of precipitated carbonates when it is discharged from carbonation unit 10.

[0113] The carbonate-laden slurry 18 is then separated in separation unit 20 into a solid phase 24 containing precipitable carbonates and an aqueous phase 28, which are discharged from separation unit 20 via solids outlet 26 and liquid outlet 30, respectively.

[0114] In some embodiments, when aqueous phase 28 is discharged from separation unit 20, it is substantially free of precipitated carbonates therein. The aqueous phase 28 may then be fed to a precipitation unit 32 via a liquid inlet 33 .

[0115] The method may include precipitating at least a portion of the precipitable carbonates of the aqueous phase 28 into alkaline earth metal carbonates in a precipitation unit 32, thereby producing a precipitation slurry 38 including the alkaline earth metal carbonates that is discharged from the precipitation unit 32 via a slurry outlet 40.

[0116] It should be appreciated that the aqueous slurry 4 containing the alkaline earth metal-containing material 6 may be formed prior to being fed to the carbonation unit 10, as shown in FIG. 2, but may also be formed directly in the carbonation unit 10 by separately feeding the alkaline earth metal-containing material 6 and water 8 to the carbonation unit 10.

[0117] In some optional aspects, the method may further include agitating the aqueous slurry in the carbonation unit to enhance contact between the carbon dioxide-containing gas and the alkaline earth metal-containing material. Agitation can be ensured by a mechanical stirrer, such as a propeller, having an agitation speed of about 400 rpm to about 800 rpm, optionally about 500 rpm to about 650 rpm.

[0118] It should be understood that the stirring step is not limited to mechanical stirring, but can include a variety of known suitable stirring techniques, such as gas fluidization.

[0119] In other optional aspects, the method may also include the step of agitating the aqueous phase in the precipitation unit to promote precipitation of the alkaline earth metal carbonate.

[0120] In some optional embodiments, the alkaline earth metal-containing material can be mixed with water to obtain an aqueous slurry having a pulp density (also referred to as the mass concentration of total solids per liter of slurry) of 25 g / L to 300 g / L.

[0121] A low pulp density may favor the dissolution of alkaline earth metals in the aqueous slurry. The effect of the density of the aqueous slurry on the carbon dioxide removal efficiency is shown in Example 2.

[0122] In some optional embodiments, the method may include thermally pretreating the alkaline earth-containing material to effect dehydroxylation.

[0123] The alkaline earth-containing material may in fact contain undesirable water that is at least partially removed by the thermal pretreatment.

[0124] During the thermal pretreatment, the water evaporates and the crystal structure of the alkaline earth metal-containing material changes to a more chemically active structure, allowing better dissolution of the alkaline earth metal in the aqueous phase.

[0125] In some cases, the method can include heating the alkaline earth metal-containing material at a pretreatment temperature of about 500° C. to about 800° C. for a pretreatment time of about 10 minutes to about 60 minutes.

[0126] Optionally, the pretreatment temperature may be between about 600° C. and about 700° C., and the pretreatment time may be between about 15 minutes and about 40 minutes.

[0127] If desired, the pretreatment temperature may be low enough to avoid recrystallization of the alkaline earth metal-containing material.

[0128] The effect of thermal pretreatment on carbon dioxide removal efficiency is shown in Example 3.

[0129] In some optional embodiments, the method can include crushing and / or grinding the alkaline earth metal-containing material to increase the surface area available for contact with the carbon dioxide-containing gas and favor carbonation of the alkaline earth metal.

[0130] Optionally, the alkaline earth metal-containing material can be crushed and / or ground so that the average particle size of the material is between about 10 μm and about 45 μm, with at least about 90% of the solid particles having a particle size between about 0 μm and about 75 μm.

[0131] If desired, a crushing and / or grinding step may be carried out prior to the thermal pretreatment step, since by using material particles of reduced size, dehydroxylation may be favored.

[0132] Referring to FIG. 3, the method may include crushing and / or grinding the alkaline earth metal-containing material 6 in a crushing / grinding unit 42 to reduce the size of the alkaline earth metal-containing material particles.

[0133] The crushed and / or ground material 6 is then fed to a thermal pretreatment unit 44 for dehydroxylation thereof, as described above.

[0134] The water 8 and the pretreated material 6 may be fed separately to the carbonation unit 10 to form an aqueous slurry therein and contact the fed carbon dioxide-containing gas 2 to produce an aqueous slurry 18 containing precipitated carbonates and a carbon dioxide-depleted gas 16.

[0135] The aqueous slurry 18 is fed to a separation unit 20 for separation into an aqueous phase 28 containing precipitated carbonates and a solid phase 24 .

[0136] At least a portion 25 of the solid phase 24 may be recycled to the crushing / grinding unit 42 as at least a portion of the alkaline earth metal material 6 .

[0137] At least a portion of the aqueous phase 28 containing precipitable carbonates is fed to a precipitation unit 32 for precipitation of alkaline earth metal carbonates and production of a precipitation slurry 38 .

[0138] The precipitate slurry 38 may be fed to a second separation unit 46 for separation into an alkaline earth metal carbonate stream 50 and a liquid stream 48 .

[0139] At least a portion of the liquid stream 48 may be recycled to the carbonation unit 10 as at least a portion of the water 8 .

[0140] In some optional embodiments, the step of precipitating the alkaline earth metal carbonate can be carried out at a precipitation temperature of about 20° C. to about 80° C., and a precipitation time of about 0.5 hours to about 12 hours, with or without stirring.

[0141] In some optional embodiments, the alkaline earth metal carbonate precipitate produced by the present method has a purity of 90-99.9%.

[0142] In some optional embodiments, the carbon dioxide-containing gas may be continuously fed to the carbonation unit while maintaining a particular or desired carbon dioxide removal efficiency (see Example 5).

[0143] Optionally, the process may be operated according to a series of batch operations including a recycle stream to increase the carbonation rate of the solid material (see Example 6).

[0144] For example, a recycle process scenario can be implemented in which the same portion of alkaline earth material is contacted with several portions of carbon dioxide-containing gas prior to precipitation to alkaline earth metal carbonate.

[0145] In some optional aspects, the method may include recycling the solid phase separated from the carbonate charge slurry to produce a fresh portion of the aqueous slurry for contacting with the carbon dioxide-containing gas in the carbonation unit.

[0146] Note that recycle is also referred to herein as recycling.

[0147] FIG. 4 shows a schematic method diagram of the various steps involved in the recirculation of various liquid and solid streams according to an optional embodiment of the present invention.

[0148] While the carbon dioxide containing gas is fed to the carbonation unit continuously or in batch mode, multiple streams may actually be recycled to the carbonation unit.

[0149] Batch Mode Gas Supply In some optional aspects, carbon dioxide-containing gas may be provided to the carbonation unit via a carbon dioxide-containing gas portion.

[0150] Step 1: A first portion of the carbon dioxide-containing gas, referred to as "Gas 1," is contacted in a carbonation unit for a specified period of time with an aqueous slurry resulting from the combination of "Solids 1" and "Liquid."

[0151] For example, the aqueous slurry may have a mass concentration of 150 g / L in the alkaline earth metal-containing material, and the aqueous slurry may be contacted with each carbon dioxide-containing gas portion for 30 minutes. After each contact step of 30 minutes, the resulting carbonate-loaded slurry is separated into a solid phase and an aqueous phase. It is noted that the first portion of gas "Gas 1" may be provided as two subportions, for example, to meet pressure limitations. Thus, two subportions of gas, each contacting the solid for 15 minutes, may be fed consecutively to the carbonation unit. From the mass balance between the carbon dioxide-containing gas and the carbon dioxide-depleted gas, a maximum of 5.91 g CO2 / L (1.64 g C / L of gas) of gas was treated after each contact step of 30 minutes.

[0152] Step 2: The aqueous phase is then fed to a precipitation unit and once the alkaline earth metal carbonate has been sufficiently precipitated, the precipitation slurry is separated into a solids stream and an aqueous stream.

[0153] Step 3: The aqueous stream is then recycled to the carbonation unit as "liquid."

[0154] The above three steps 1-3 are repeated two more times to contact the second and third portions of the carbon dioxide-containing gas, referred to as "Gas 2" and "Gas 3." After contact with "Gas 2" and "Gas 3", the solid phase "Solid 1" is dried, ground and heated in a pretreatment unit as previously described.

[0155] Steps 1-3 are performed three more times using the ground and heated solid phase "Solid 1", successively contacting "Gas 4", "Gas 5" and "Gas 6".

[0156] After contact with six carbon dioxide-containing gas portions ("Gas 1" through "Gas 6"), the solid phase reaches its reactivity limit.

[0157] All of the above method steps can then be repeated with a new portion of alkaline earth metal-containing material.

[0158] Continuous Mode Gas Supply In some other optional embodiments, the carbon dioxide containing gas stream may be continuously fed to the carbonation unit.

[0159] In batch mode, the important parameter to be controlled was the contact time of the portion of carbon dioxide-containing gas, or in continuous mode, the important parameter to be controlled was the amount of dissolved carbon dioxide in the aqueous slurry.

[0160] According to the above example of batch mode operation, a maximum of 5.91 g CO2 / L of gas (1.64 g C / L of gas) was treated after each contact step of 30 minutes.

[0161] Considering that all of the treated carbon dioxide is dissolved in the aqueous slurry, the maximum concentration of dissolved carbon dioxide should not exceed about 5.0 g C / L, as precipitation may occur in the reactor.

[0162] Thus, in continuous mode, when a concentration of 5.0 g C / L of dissolved carbon dioxide is measured in the aqueous slurry, the aqueous slurry is removed from the carbonation unit and separated into solid and aqueous phases.

[0163] The aqueous phase is then fed to a precipitation unit.

[0164] Optionally, depending on the precipitation rate of the alkaline earth metal carbonate in the precipitation unit, a certain amount of water can be fed to the aqueous phase to maintain a low dissolved carbon dioxide concentration in the recirculating aqueous phase along the process.

[0165] For example, when the cumulative amount of treated carbon dioxide reaches 16.04 g CO2 / L of gas (4.4 g C / L of gas), the separated solid phase is dried, crushed, heated, and then reused.

[0166] Therefore, steps 1-3 are again performed sequentially following the same scenario described above, reaching a cumulative amount of treated carbon dioxide of approximately 27.28 g CO2 / L gas (7.47 g C / L gas) for the overall series of the three steps 1-3.

[0167] A fresh portion of the alkaline earth metal-containing solid may then be used.

[0168] It is to be understood that any one of the above-mentioned aspects of each of the methods, methods, systems, uses, and materials can be combined with any other aspect of those aspects, unless the two aspects cannot clearly be combined because they are mutually exclusive.

[0169] For example, the various operational steps of the methods described herein above, herein below, and / or in the accompanying drawings may be combined with any of the methods, systems, or instructions for use described in this specification and / or the accompanying claims.

[0170] It is also understood that the various parameter values ​​obtained and / or described in any of the examples, tables, and descriptions herein can be considered as maximum, minimum, or intermediate values, and that various ranges can be derived from these maximum, minimum, or intermediate values, as described herein or in the accompanying drawings and claims.

[0171] In some embodiments, the MgO production process comprises a preceding method for producing magnesium carbonate and sequestering carbon dioxide from a carbon dioxide-containing gas.

[0172] The method may include contacting a carbon dioxide containing gas with an aqueous slurry comprising an alkaline earth metal-containing material in a carbonation unit for carbonating at least a portion of the alkaline earth metal to produce a carbon dioxide depleted gas and a carbonate loaded slurry comprising precipitable carbonates and substantially free of precipitated alkaline earth metal carbonates, removing the carbonate loaded slurry from the carbonation unit and separating the carbonate loaded slurry into an aqueous phase comprising precipitable carbonates and a solid phase, and feeding the aqueous phase to a precipitation unit and precipitating the alkaline earth metal carbonates in the precipitation unit to produce a precipitated slurry.

[0173] In some embodiments, the aqueous phase may contain precipitated carbonates and may be substantially free of precipitated alkaline earth metal carbonates.

[0174] In some embodiments, the method may further comprise the step of agitating the aqueous slurry comprising the alkaline earth metal-containing material during the contacting step in the carbonation unit.

[0175] Optionally, the process may include the step of agitating the aqueous phase during the step of precipitating the alkaline earth metal carbonate in the precipitation unit.

[0176] In some embodiments, the method may further comprise, prior to the contacting step, mixing the alkaline earth metal-containing material with water to dissolve the alkaline earth metal ions in the aqueous phase and form an aqueous slurry.

[0177] In some embodiments, the method further comprises mixing and simultaneously contacting the alkaline earth metal-containing material with water to dissolve the alkaline earth metal ions in the aqueous phase and form an aqueous slurry in the carbonation unit.

[0178] Optionally, the mixing step can be carried out to form an aqueous slurry having a mass concentration of between 25 g / L and 300 g / L in grams of total solids per liter of aqueous slurry.

[0179] In some embodiments, the method may further comprise separating the precipitation slurry into a solids stream comprising the alkaline earth metal carbonate and an aqueous stream.

[0180] In some embodiments, the method may further comprise the step of drying the solids stream comprising the alkaline earth metal carbonate.

[0181] In some embodiments, the method may further include recycling at least a portion of the aqueous stream to the carbonation unit.

[0182] In some embodiments, the method may further include recycling at least a portion of the solid phase to the carbonation unit as at least a portion of the alkaline earth metal-containing material for contacting with the carbon dioxide-containing gas.

[0183] In some embodiments, the method may further include thermally pretreating the alkaline earth metal-containing material to effect its dehydroxylation and produce a pretreated alkali earth metal-containing material for contacting with the carbon dioxide-containing gas.

[0184] Optionally, the step of thermally pretreating the alkaline earth metal-containing material can include heating the alkaline earth metal-containing material at a temperature of about 500° C. to about 800° C. for a pretreatment time of about 10 minutes to about 60 minutes.

[0185] Optionally, the temperature may be between about 600° C. and about 700° C., and the pretreatment time may be between about 15 minutes and about 40 minutes.

[0186] In some embodiments, the method may further comprise the step of crushing and / or pulverizing the alkaline earth-containing material prior to the step of contacting with the carbon dioxide-containing gas.

[0187] If desired, a crushing and / or grinding step may be carried out prior to the step of thermally pre-treating the alkaline earth metal-containing material.

[0188] Further optionally, a crushing and / or grinding step may be performed to obtain solid particles having a median particle size of about 10 μm to about 45 μm, with 90% of the solid particles having a particle size of about 0 μm to about 75 μm.

[0189] In some embodiments, the carbon dioxide containing gas may be derived from industrial emissions and may have a carbon dioxide concentration between 1% and 30%.

[0190] In some embodiments, the method may further include controlling at least one of the carbonation temperature, agitation speed, and carbonation pressure in the carbonation unit.

[0191] In some cases, the contacting step in a carbonation unit can be carried out at a carbonation temperature between about 10°C and about 40°C.

[0192] Optionally, the carbonation temperature may be between about 20°C and about 30°C.

[0193] In some cases, the contacting step in the carbonation unit can be carried out at a carbonation pressure of from about 1 bar to about 20 bar.

[0194] Optionally, the carbonation pressure may be between about 2 bar and about 12 bar. Optionally, the agitation speed in the carbonation unit may be between about 400 rpm and about 800 rpm, and further optionally, may be between about 500 rpm and about 650 rpm.

[0195] In some embodiments, the precipitating step can be carried out at a precipitation temperature of about 20° C. to about 80° C. for a precipitation time of about 0.5 hours to about 12 hours. Optionally, the precipitating step can include agitating the aqueous phase.

[0196] In some embodiments, the alkaline earth metal-containing material comprises sandstone, granite, anorthosite, basalt, serpentine, peridotite, serpentinized peridotite, ophiolite rocks, mafic and ultramafic rocks, rocks containing more than 10% pyroxene and peridot, calcium silicate, magnesium silicate, feldspar, plagioclase, feldspar, pyroxene, olivine, serpentine, wollastonite, calcium oxide, magnesium oxide, brucite, mafic and ultramafic minerals, steel slag, MgO bricks for steel, rotary kiln dust (CKD, LKD) waste cement, waste concrete, construction and demolition waste, concrete with aggregate, concrete bricks, concrete, red bricks, phyllosilicate mine residues, and chrysotile mine residues.

[0197] In some embodiments, the alkaline earth metal can include calcium or magnesium.

[0198] In some embodiments, the method may further include the step of continuously supplying a carbon dioxide-containing gas to a carbonation unit.

[0199] In some cases, the method may include controlling or managing a maximum amount of dissolved carbon dioxide in the carbonate load slurry produced in the carbonation unit, the maximum amount of dissolved carbon dioxide being selected to reduce or avoid precipitation of alkaline earth metal carbonate in the carbonation unit.

[0200] In some cases, the maximum amount of dissolved carbon dioxide may be up to 5 g / L. In some embodiments, the carbon dioxide containing gas can include a plurality of carbon dioxide containing gas portions, and the method includes: providing at least one carbon dioxide-containing gas portion to a carbonation unit; contacting an aqueous slurry with the at least one carbon dioxide-containing gas portion in the carbonation unit to produce a carbonate-loaded slurry; removing the carbonate-loaded slurry from the carbonation unit and separating the carbonate-loaded slurry into an aqueous phase including precipitated carbonates and a solid phase; recycling the solid phase to the carbonation unit and providing water to the carbonation unit to form a new portion of the aqueous slurry; and contacting the new portion of the aqueous slurry with another carbon dioxide-containing gas portion to produce a carbonate-loaded slurry.

[0201] In some embodiments, the carbon dioxide containing gas may be supplied to the carbonation unit in multiple carbon dioxide containing gas portions, the method including: contacting the carbonate loaded slurry with at least one carbon dioxide containing gas portion to produce a carbonate loaded slurry; removing the carbonate loaded slurry from the carbonate loading unit and separating the carbonate loaded slurry in a precipitation unit; precipitating the alkaline earth metal carbonate in the precipitation unit to produce a precipitation slurry and separating the precipitation slurry into a solids stream comprising the alkaline earth metal carbonate and an aqueous stream; recycling the solids and the aqueous stream to the carbonate loading unit to produce a new portion of the aqueous slurry, and contacting the new portion of the aqueous slurry with another carbon dioxide containing gas portion to produce a carbonate loaded slurry.

[0202] Optionally, the method may include supplying water to the carbonation unit as a make-up stream for the fresh portion of the aqueous slurry.

[0203] In some embodiments, the contacting step in the carbonation unit may be performed for a maximum gas contact time, which is controlled or managed to reduce or avoid precipitation of alkaline earth metal carbonate in the carbonation unit.

[0204] Optionally, the maximum gas contact time may be between about 1 minute and about 60 minutes. In some embodiments, the method may also include the step of crushing and / or grinding the solid phase prior to recycling to the carbonation unit to generate a new portion of the aqueous slurry.

[0205] In some embodiments, a method for sequestering carbon dioxide from a carbon dioxide-containing gas is provided.

[0206] The method includes contacting a carbon dioxide containing gas with an aqueous slurry containing magnesium-containing material in a carbonation unit at a carbonation pressure of from about 1 bar to about 20 bar and a carbonation temperature of from about 10° C. to about 40° C. to carbonate at least a portion of the magnesium to produce a carbon dioxide depleted gas and a carbonate-loaded slurry containing precipitated carbonates and substantially free of precipitated magnesium carbonate.

[0207] In some embodiments, the method may include removing the carbonate loaded slurry from the carbonation unit; separating the carbonate loaded slurry into a solid phase and an aqueous phase comprising precipitable carbonates and substantially free of precipitated magnesium carbonate; and feeding the aqueous phase to a precipitation unit where the magnesium carbonate is precipitated to produce a precipitation slurry comprising precipitated magnesium carbonate.

[0208] In some embodiments, the method may further comprise separating the precipitated slurry into a solids stream containing the precipitated magnesium carbonate and an aqueous stream.

[0209] In some embodiments, a method for sequestrating carbon dioxide from a carbon dioxide-containing gas is provided, the method comprising contacting an alkaline earth metal-containing material in a substantially dry form with a carbon dioxide-containing gas in at least one carbonation unit at a carbonation temperature between about 200° C. and about 500° C. and a carbonation pressure between about 1 bar and about 20 bar for carbonation thereof to produce carbonate and a carbon dioxide-depleted gas.

[0210] In some embodiments, a method is provided for sequestering carbon dioxide from an industrial effluent by contacting the industrial effluent with a magnesium silicate material, in wet or dry form, to produce a carbon dioxide depleted gas and a magnesium carbonate silicate material.

[0211] In some embodiments, a method for producing an alkaline earth metal carbonate is provided, comprising: a contacting step of contacting an industrial effluent containing carbon dioxide with an aqueous slurry containing alkaline earth metal-containing material to produce a carbon dioxide depleted gas and an alkaline earth metal carbonate stream substantially free of precipitated alkaline earth metal carbonate; a precipitation step of precipitating alkaline earth metal carbonate from the alkaline earth metal carbonate stream to produce a precipitate slurry; and a separation step of separating the precipitate slurry into precipitated alkaline earth metal carbonate and an aqueous phase.

[0212] In some embodiments, a method for producing an alkaline earth metal carbonate is provided, comprising: a contacting step of contacting an industrial effluent comprising carbon dioxide with an aqueous slurry comprising alkaline earth metal-containing material to produce an alkaline earth metal carbonate stream comprising carbon dioxide depleted gas and precipitable carbonates and substantially free of precipitated alkaline earth metal carbonates; a first separation step of separating the alkaline earth metal carbonate stream into a solid phase comprising precipitable carbonates and substantially free of precipitated alkaline earth metal carbonates and an aqueous phase; a recycle step of recycling the solid phase as at least a portion of the alkaline earth metal-containing material to the carbonation step, thereby producing a precipitate slurry comprising precipitated alkaline earth metal carbonates; and a separation step of separating precipitated alkaline earth metal carbonates and an alkaline earth metal carbonate slurry.

[0213] In some embodiments, a carbon dioxide sequestration system is provided for sequestering carbon dioxide from a carbon dioxide-containing gas.

[0214] The system includes at least one carbonation unit having: a gas inlet for receiving a carbon dioxide containing gas, a slurry inlet for receiving an aqueous slurry comprising an alkaline earth metal containing material, a carbonation vessel for carbonate at least a portion of the alkaline earth metals of the aqueous slurry with carbon dioxide to produce a carbon dioxide depleted gas, and a carbonate load slurry comprising precipitable carbonates and substantially free of precipitable alkaline earth metal carbonates, a slurry outlet for discharging the carbonate load slurry comprising precipitable carbonates, and a gas outlet for discharging the carbon dioxide depleted gas; a slurry inlet for receiving a carbonate load slurry comprising precipitable carbonates from the slurry outlet of the at least one carbonation unit, a separation chamber for separating the carbonate load slurry comprising precipitable carbonates into a solid phase and an aqueous phase comprising precipitable carbonates and substantially free of precipitated alkaline earth metal carbonates, a liquid outlet for releasing the aqueous phase, and a solid outlet for releasing the solid phase; and a precipitation unit having: a slurry inlet for receiving an aqueous phase comprising precipitable carbonates from the liquid outlet of the separation unit, a precipitation chamber for precipitation of alkaline earth metal carbonates and formation of a precipitate slurry, and a liquid outlet for discharging the precipitate slurry.

[0215] In some embodiments, there is provided the use of a magnesium-containing material in the form of an aqueous slurry for contacting with a carbon dioxide-containing gas at a temperature of about 20° C. to about 30° C. and a pressure of about 2 bar to about 12 bar to sequester carbon dioxide from the carbon dioxide-containing gas to form magnesium carbonate.

[0216] In some embodiments, there is provided the use of phyllosilicate mine residues to sequester carbon dioxide from industrial emissions and produce magnesium carbonate.

[0217] Optionally, the phyllosilicate mining residue comprises at least one of lizardite, antigorite, brucite, iron oxide, chromium oxide, and white asbestos.

[0218] In some embodiments, precipitated calcium or magnesium carbonate (PCC or PMC) is provided that is produced by contacting a calcium or magnesium containing material in wet form with carbon dioxide from an industrial effluent in a carbonation unit to form a carbonate loaded slurry, and precipitating the calcium or magnesium carbonate from the carbonate loaded slurry in a precipitation unit.

[0219] In some embodiments, precipitated calcium or magnesium carbonate (PCC or PMC) is provided that comprises at least 95% by weight calcium or magnesium carbonate in dry or hydrated form.

[0220] It should also be noted that a higher CO2 content in the calcination exhaust gas favors the carbonation reaction, increasing the overall process efficiency.

[0221] Calcination can optionally be engineered to obtain higher CO2 contents, for example, by operating the calcination unit at particular operating conditions and using particular reactants.

[0222] For example, in some embodiments, the calciner unit can be operated to increase the CO2 concentration in the exhaust by ensuring complete combustion of the natural gas or other combustibles used, which can include providing excess preheated air to promote complete combustion and reduce consumption of combustibles.

[0223] The air supply rate can be controlled accordingly and the calcination unit can be properly sealed to minimize the introduction of other gases that may dilute the system.

[0224] Additionally, the calcination unit can be operated by increasing the oxygen content in the gas feed, thereby decreasing the concentration of other gas components that may be present in the air.

[0225] Oxygen levels can be provided and / or the calcination unit can be otherwise operated such that the resulting exhaust has a higher CO2 content than the CO2 content of the flue gas supplied to the carbonation unit.

[0226] In this way, recycling of CO2 from the calcination back to the carbonation process can increase the CO2 concentration, thereby enhancing overall performance.

[0227] In some examples, the CO2 concentration in the recirculated exhaust can be at least 1%, 2%, 5%, 10%, 15%, 20%, 25%, 30%, 40% or 50% higher than the CO2 concentration in the flue gas.

[0228] In some embodiments, the method includes contacting the CO2-containing stream with a magnesium-containing material to produce magnesium carbonate; calcining the magnesium carbonate to produce a CO2-containing gas by-product and magnesia, the CO2-containing gas by-product having a higher CO2 concentration than the CO2-containing stream; and recycling at least a portion of the CO2-containing gas by-product for contact with the magnesium-containing material to produce magnesium carbonate. The CO2-containing stream may be from a first emission source, which may be flue gas (e.g., from a power plant or other emitter). The CO2-containing stream may have a CO2 content of, for example, 10% to 20% by weight. The CO2-containing gas by-product may have a higher CO2 content, which may be several percent higher (e.g., 12 wt% to 22 wt% CO2) or substantially higher (e.g., 30 wt%, 40 wt%, 50 wt%, or approaching 100 wt% CO2).

[0229] It should be noted that a preferred operation is to provide the CO2-containing gas by-product with a CO2 content that is a percentage (e.g., 10% to 50%) higher than the CO2 content of the CO2-containing stream. For example, the CO2-containing stream may have a CO2 content of about 15% by weight, while the CO2-containing gas by-product may have a CO2 content of about 18% by weight (20% higher).

[0230] This can be accomplished without the added expense of operating the calcination unit with pure oxygen, but rather using control of the calcination unit's operating parameters.

[0231] Nevertheless, it should be noted that in alternative embodiments, the process can be operated such that the recycled CO2-containing gas by-product has a lower CO2 concentration, or generally similar CO2 content, compared to the original CO2-containing flue gas fed to the carbonation step.

[0232] If relatively variable CO2 content is found in the two gas streams, the relative ratio can be altered to obtain a constant CO2 content fed to the carbonation unit, or the two streams can be fed to carbonation without concentration control, resulting in a variable CO2 content in the reaction gas.

[0233] It should also be noted that the two CO2-containing streams can be fed to the same carbonation vessel, or to separate carbonation vessels, or a combination thereof, via different feed inlets or the same feed inlet. EXAMPLES

[0234] Examples and Experiments Experiment 1: Wet carbonation of white asbestos mine residue A first series of experiments was carried out to optimise the conditions for wet carbonation with a sample size of about 7 g with a particle size below 75 μm and a pulp density of 15% (mass of 150 g solids per litre of liquid) using white asbestos mining residues consisting of lizardite, antigorite, brucite, iron oxide, chromium oxide and low content of white asbestos. The temperature and reaction time were kept stable at 25° C. and 6 hours, respectively.

[0235] The parameters that can be varied are pressure, NaCl and NaHCO3 content, and whether or not the sample is heat treated.

[0236] They were optimized based on the percentage of CO2 removal and the percentage of solid carbonate formed (dependent variables).

[0237] The various conditions and the results obtained are shown in Table 1.

[0238] From this table it is clear that for 10.2 atm pressure and heat treated samples, up to 87% CO2 removal can be achieved. CO2 removal appears to be independent of NaCl content and slightly dependent on the NaHCO3 content in the solution, but heat pretreatment is required. At these conditions, 24% of the sample was carbonated in the 6 hour experiment.

[0239] [Table 1]

[0240] The 6-h duration of carbonation at optimal conditions was very long, and carbonation assays were performed at shorter reaction times to verify the time dependence of wet carbonation rate.

[0241] The experimental conditions and results are shown in Table 2. The temperature is kept constant at 25°C and the pulp density is kept constant at 15%.

[0242] [Table 2]

[0243] 82% removal of CO2 was achieved after 30 min of reaction time.

[0244] Experiment 2 - Wet carbonation of serpentine This experiment describes the feasibility of the method for treating a batch of gas containing 18.2% carbon dioxide for 15 minutes.

[0245] The gas-liquid ratio (GLR) was fixed at 300% with a volume of 225 mL of carbon dioxide-containing gas and 75 mL of water. The resulting aqueous slurry had a concentration of solid material of 15% by weight. The reaction temperature was set at ambient temperature (18-25 °C). A pressure of 10.5 bar was applied, which represented an amount of 0.78 g of CO2 at 20 °C. Once the pressure was reached, all valves of the reactor were closed and the reaction was carried out for 15 min.

[0246] The resulting carbon dioxide depleted gas was then sampled through the bag. The carbon dioxide concentration in the carbon dioxide depleted gas was measured by a CO2 analyzer. The resulting aqueous slurry was filtered and a sample was taken for analysis.

[0247] Reactions at ambient temperature and 10.5 bar for 15 minutes showed an efficiency of 88+ / -1% for CO2 removal, as seen in Table 3.

[0248] [Table 3]

[0249] Experiment 3 - Optimization of thermal pretreatment of serpentine prior to wet carbonation Another series of experiments was carried out to show that the thermal pretreatment of alkaline earth metal-containing material is favorable for the better removal of carbon dioxide from carbon dioxide-containing gas. Serpentine-based mining residues were used as the alkaline earth metal-containing material.

[0250] The residue was first crushed and then ground depending on the particle size. The best results were obtained with samples with a particle size below 45 μm (median size 10 μm).

[0251] To obtain chemically reactive materials, serpentine-based mining residues must be further pretreated to allow dehydroxylation of the serpentine. By removing water from the various crystal structures of the minerals, the chemical structure of the sample is changed and therefore the binding energy is reduced. It is well known that thermal activation of hydrated silicates is favorable for chemical activation before leaching [Nagamori et al.(1980)Activation of magnesia in serpentine by calcination and chemical utilization of asbestos tailing-A review. CIM Bulletin 73, pp. 144-156].

[0252] Optimization of the thermal pretreatment was performed according to the magnesium concentration after leaching dissolved in water (beaker). With reference to Figures 5 and 6, the effect of temperature and pretreatment time, as well as pulp density, during extraction in water for 30 minutes with stirring at 600 rpm was investigated. According to thermogravimetric analysis, the main weight loss of the tested samples is observed at 650°C. A paper on thermal activation showed that the best results were obtained after 30 minutes of treatment at 650°C, with a mass loss of about 10%.

[0253] Experiment 4 - Optimization of reaction parameters for wet carbonation Another series of experiments was carried out to optimize the reaction parameters including carbonation pressure, reaction time, gas / liquid ratio (GLR) and pulp density of the aqueous slurry. To increase the solubility of gaseous carbon dioxide in water, the reaction temperature was set at room temperature (18-25 °C) as the solubility increases at lower temperatures. Pressure is an important process parameter as it affects the amount of carbon dioxide introduced into the reactor.

[0254] The experiments were carried out using carbon dioxide-containing gas whose properties are comparable to cement plant flue gas: 18.2% CO2, 4.11% O2, and 77.69% N2, respectively. The reactions were realized in a 300 mL stirred reactor manufactured by Parr Instrument Company (Moline IL USA).

[0255] pressure Tests on pressure effects showed that working at low pressure did not affect the reaction efficiency. In fact, lowering the pressure introduces a small amount of carbon dioxide into the reactor. In the batch experiments, the pressure was set at 10.5 bar to maintain a given amount of carbon dioxide introduced into the reactor.

[0256] GLR and pulp density Parameters like gas / liquid ratio (GLR) and pulp density were determined by a set of experiments with a reaction time of 30 minutes. Decreasing the GLR did not affect the removal of carbon dioxide from the flue gas, but it reduced the amount of carbon dioxide introduced into the reactor. On the other hand, when the pulp density was set at 5%, the amount of treated flue gas was less. To increase the amount of treated gas, the experiments on GLR and pulp density were carried out with successive batches of gas.

[0257] Since the objective is to form alkaline earth metal carbonates with the potential for resale, it is important to have the purest final product possible. Experiments with 100% GLR and 15% pulp density showed that a significant amount of carbonate precipitated in the reactor. However, it may be desirable to precipitate the carbonate outside the reactor in order to easily separate the precipitable carbonate and subsequently obtain a high purity carbonate of about 95%. Figure 7 shows that with an aqueous slurry of 15% pulp density and 300% GLR, good yields of CO2 removal and high concentrations of magnesium in solution are encountered. Once the main parameters of the reaction were stabilized, the reaction time was reduced.

[0258] Reaction time A series of experiments were performed to reduce the reaction time. The carbon dioxide removal results are shown in Figure 8. The removal was 56% for a 5 minute reaction time and 83% for a 10 minute reaction time. The same efficiency observed for 30 minutes was achieved in 15 minutes. However, the amount of magnesium present in the solution is multiplied by 1.45, 341 mg / L for 30 minutes, respectively, versus 495 mg / L for 15 minutes. A 15 minute residence time is reasonable for industrial applications and provides a better efficiency for magnesium solubilization.

[0259] Experiment 5 - Wet carbonation of zinc ore under continuous operation The experiment was carried out under continuous conditions. The purpose was to confirm the feasibility of the reaction under mild pressure and temperature conditions. The carbon dioxide-containing gas flow was regulated by a mass flow controller. The pressure in the reactor was controlled by a pressure gauge valve set at the desired pressure.

[0260] The experiment was carried out at 3.4 bar with a carbon dioxide-containing gas flow of 42 mL / min (7.64 mL CO2 / min). With reference to FIG. 9, after an equilibrium phase of about 50 min, the efficiency of carbon dioxide removal was observed to remain constant at above 98% for 130 min. After that, the efficiency decreased according to a linear trend. Finally, the total amount of carbon dioxide reacted was 2.61 g CO2 out of 3.19 g CO2 introduced. The total leaching of magnesium was 50.8% compared to the initial magnesium content of the material introduced into the reactor.

[0261] Test 6 - Recirculation Scenario The recycle scenario is based on treating multiple "batches" of carbon dioxide-containing gas with recycle solid and liquid streams. The experiments were carried out on a series of 6 batches of gas under the same conditions defined in Example 2. The term "batch" is defined herein by 225 ml of gas (0.78 g CO2) at 10.5 bar reacting for 15 minutes under 600 rpm agitation.

[0262] The aqueous slurry consisted of 15% solids in 75 ml of water and was contacted with two batches of carbon dioxide-containing gas and then filtered into solid and aqueous phases. The same filtered solid phase was again mixed in 75 ml of "fresh" water (or recycled water) and contacted with two more batches of carbon dioxide-containing gas. This operation was repeated for a total of six batches of carbon dioxide-containing gas. After each filtration, the filtered aqueous stream, rich in dissolved magnesium and carbon dioxide, was fed to a precipitator for precipitation of magnesium carbonate.

[0263] The precipitation conditions were set at 40° C. under 300 rpm agitation. The filtered solid phase was contacted with 6 batches of carbon dioxide-containing gas, then crushed and heated to improve further magnesium leaching. The treated solid phase was then recycled in the reactor for further contact with 6 batches of carbon dioxide-containing gas. Thus, a total of 12 batches of carbon dioxide-containing gas were treated with the same solid phase.

[0264] The aqueous phase was filtered after contacting two batches of carbon dioxide-containing gas, and fresh water was used after contacting two batches of carbon dioxide-containing gas. The results are summarized in Table 4. Assuming that all the magnesium contained in the aqueous phase has precipitated, the carbonization of the solid material after contact with 12 batches is 64%.

[0265] [Table 4]

[0266] Experiment 7: Dry gas-solid carbonation Example 7 describes dry gas-solid carbonation experiments according to optional embodiments of the present invention.

[0267] In this series of experiments, the alkaline earth metal-containing material was white asbestos mine residue coming from the Tetford mine area directly from the outlet of the residue conveyor. The white asbestos residue was crushed and ground to a mini particle size of about 50 microns. The reaction was carried out in a Parr Instrument Company mini bench top reactor 4560. After the reaction, the gas was sampled in a 3.8 L Tedlar Bag equipped with an on / off valve.

[0268] Carbon dioxide concentration in the outlet gas was measured using a CO2, Quantek Instruments, model 906. Optimization of different parameters that can have a significant effect on direct dry gas-solid carbonation was performed both by traditional single variable at a time and by statistical response surface methodology.

[0269] Parameter optimization using traditional single variable methods A series of experiments were conducted to optimize the most suitable conditions for direct dry gas-solid carbonation with conventional single variable change at a time. Carbonation performance at different temperatures and pressures was optimized based on the percentage of CO2 removal (dependent variable). The optimized conditions were evaluated for raw, non-magnetic (Non-Mag) and heat-treated samples. The optimized conditions for each type of sample are shown in Table 5.

[0270] [Table 5]

[0271] The operating conditions for direct dry carbonation were optimized for 6 h at 5 atm and temperature of 200 C. The maximum CO2 removal rate of 36.8% was obtained for untreated and heat-treated (630 C for 30 min, crushed) samples.

[0272] Parameter optimization using Box-Behnken design The independent variables selected were temperature (X1), pressure (X2) and time (X3), and the independent response variables selected were CO2 removal, Y1 (%) and pressure variation, Y2 (kPa). This study focused on the CO2 removal rate since CO2 removal is the key factor in this experiment. Therefore, the percentage of CO2 removal was selected as the primary response surface in this model. 25 g of heat-treated (630°C, 30 min) samples were used for all experiments.

[0273] Figure 10 shows the response surface graph of CO2 removal (%), from which it is clear that CO2 removal (%) is maximum in the low pressure and high temperature region. The optimum conditions and validation of the optimized values ​​are shown in Table 6. The analysis of variance of the quadratic regression parameters for the predicted response surface of CO2 removal (%) was analyzed by ANOVA.

[0274] The model F value is 30.56 and the low probability value "Prob>F" is less than 0.050, which means that the model is significant. 2 = 0.9752) indicates that only 2.5% of the total variation could be explained by the empirical model. The model was able to explain 97.5% of the variability in the response. R 2 (0.9752)(%) is the adjusted R 2 The predicted R 2 (0.70) is the adjusted R 2 was reasonably consistent with

[0275] The optimum conditions for direct dry gas-solid carbonation by Box-Behnken design were obtained at 258°C, 5.6 atm, and 310 min, and a CO2 removal of 40.1% was predicted at the above conditions. Model validation shows a CO2 removal of 37%, close to the predicted value.

[0276] [Table 6]

[0277] Carbonation studies were also carried out with raw and non-magnetic samples at optimized conditions obtained from response surface methodology. The experiments and results are shown in Table 7, which show that the CO2 removal (%) of the three samples is in a close range at the optimized conditions. This indicates that sample pretreatment does not significantly affect the CO2 removal (%).

[0278] [Table 7]

[0279] Because the carbonation time under optimal conditions seems to be very long at 310 min, carbonation assays were performed with shorter reaction times to verify the time dependence of the dry carbonation rate. The experiments and results are shown in Table 8.

[0280] [Table 8]

[0281] The results showed that the major percentage of the reaction occurs in the early stages of the carbonation reaction. The reaction achieved about 36% CO2 removal at 258 °C and 5.53 atm within 15 minutes. This may suggest that the majority of the carbonation occurs within a time frame when the reaction becomes less significant.

[0282] The pressure change curves shown in Figure 11 support the above explanation. The sudden decrease in pressure in the first few minutes indicates that the reaction occurs rapidly at first, and then the decrease in pressure that becomes very slow or constant indicates that the carbonation becomes very slow or reaches equilibrium. The increase in pressure and temperature immediately after the addition of the CO2 gas mixture may be due to the exothermic nature of the reaction. The decrease in reaction rate after a certain time may be due to the formation of a product layer, which further impedes the inward diffusion of CO2 and the outward diffusion of water. A lower surface renewal rate can also decrease the carbonation rate, which can be increased by increasing the rate of particle attrition and abrasion due to well mixing.

[0283] Experiment 8-Comparison of CO2 removal efficiency Experiments were conducted to compare the CO2 removal efficiency for wet and dry carbonation of various alkaline earth metal-containing materials. The results of wet carbonation are shown in Table 9, and the results of dry carbonation are shown in Table 10.

[0284] [Table 9]

[0285] [Table 10]

[0286] Test 8: Magnesia production The following results illustrate the advantages of the magnesia production method described herein compared to conventional methods.

[0287] Based on the technical simulation carried out using the experimental data obtained from the serpentine carbonation process, the following data was obtained:

[0288] Zero CO2 losses were assumed from the entire MgCO3 calcination process. Calcination CO2 by-product emissions were calculated based on the total process energy demand (carbonation + calcination = 1 139 kWh / t solids) using the stoichiometry in Equation 1. No CO2-equivalent emissions (from other greenhouse gases) were considered and CO2 emissions were accounted for as representing the primary emissions in this scheme.

[0289]

number

[0290] Based on Case 2, the production of 179,000 tMgO per year can allow the treatment of 184,000 tCO2 from industrial sources, resulting in the emission of 87,000 tCO2. In comparison, a similar MgO production following conventional processes would produce 263,000 tCO2. Thus, the CO2 emission reduction is 176,000 tCO2 (263,000-87,000), resulting in a total economic benefit of 360,000 tCO2 per year (176,000+184,000).

[0291] Experiment 9 - Emissions Comparison The CO2 emissions resulting from the MgCO3 calcination process can contain 10%-23% CO2. The technology described herein using Mg silicate to generate MgCO3 from flue gas (e.g., 18.2% CO2) confirms the applicability with MgO production related CO2 emissions as described. For example, the calcination exhaust can contain similar CO2 content compared to the flue gas, and thus the carbonation step can utilize both the flue gas and the calcination exhaust as sources of CO2 with sufficient consistency for operational performance.

[0292] Experiment 10 - Carbonate Calcination This concerns the calcination of Nesquehonite (MgCO3·3H2O) produced from the technology described herein to magnesia (MgO) at 950°C. MgCO3·3H2O was generated during the precipitation step (step 32). The experiment was carried out in an electrically heated laboratory scale rotary kiln. The kiln's inner diameter and length were 44.45 mm and 1000 mm, respectively. Calcination was achieved by heating a 5.0 g material feed at a constant rate of 0.18 g / min. The control panel set the kiln speed to 3 rpm. The mass loss caused by heating was 68%. This highlighted the decomposition of Nesquehonite onto MgO with the concomitant loss of CO2 and H2O.

Claims

1. CO ２ subjecting the magnesium-containing material to carbonation to produce magnesium carbonate, comprising contacting a magnesium-containing gas with the magnesium-containing material; and Magnesium carbonate is calcined to produce CO ２ producing by-products and magnesia; and wherein subjecting the magnesium-containing material to carbonation further comprises: CO ２ At least a portion of the by-product is recycled CO ２ The magnesium-containing material is recycled as a by-product. ２ contacting the by-product; and CO ２ Recirculated CO to contained gas ２ Control the relative amounts of by-products to provide a constant CO2 feed to the carbonation ２ Obtaining the content, A method for producing magnesia comprising:

2. The CO ２ The step of contacting the magnesium-containing gas with the magnesium-containing material comprises providing the magnesium-containing material in an aqueous slurry and ２ Containing effluent and recycled CO ２ The method of claim 1 further comprising contacting the by-product with an aqueous slurry.

3. producing a carbonate charge slurry comprising precipitable carbonates and free of precipitated alkaline earth metal carbonates in the contacting step; separating the carbonate charge slurry into an aqueous phase containing said precipitable carbonate and a solid phase; precipitating said magnesium carbonate from the aqueous phase; and Separating the magnesium carbonate from the aqueous phase; The method of claim 1 or claim 2, further comprising:

4. CO ２ CO containing gas is used directly as produced from the plant ２ The method of any one of claims 1 to 3, comprising containing effluent.

5. CO ２ The method of claim 4 , wherein the contained effluent comprises effluent from another source.

6. CO ２ dehydroxylating the magnesium-containing material to reduce the moisture content of the magnesium-containing material prior to contacting the magnesium-containing gas; The method of any one of claims 1 to 5, further comprising:

7. CO from dehydroxylation ２ CO ２ 7. The method of claim 6, wherein the gas is supplied to the contacting step as part of the containing gas.

8. The magnesium-containing material comprises a plurality of CO ２ The CO containing source ２ The method according to any one of claims 1 to 7, wherein the mixture is contacted with a containing gas.

9. The CO2-containing gas is derived from an additional magnesia production train. ２ The method of claim 8 further comprising:

10. 10. The method of any one of claims 1 to 9, comprising pre-treating the magnesium-containing material prior to carbonation to produce a magnesium-containing particulate material, the magnesium-containing particulate material having between 1% and 35% by weight magnesium.

11. 11. The method of claim 10, wherein the magnesium content is between 10% and 30% by weight.

12. 12. The method of any one of claims 1 to 11, wherein the magnesium-containing material is derived from at least one of basalt, peridotite, serpentine, ophiolitic rock, mafic rock, ultramafic rocks, peridot, pyroxene, olivine, serpentinized peridotite, magnesium oxide-containing minerals, and / or brucite.

13. The method of any one of claims 1 to 11, wherein the magnesium-containing material is derived from an industrial by-product material.

14. 14. The method of claim 13, wherein the industrial by-product material comprises steelmaking slag and / or steelmaking worn magnesium oxide bricks.

15. 12. The method according to any one of claims 1 to 11, wherein the magnesium-containing material is derived from phyllosilicate mining residues and / or chrysotile mining residues.

16. 16. The method of any one of claims 1 to 15, further comprising: reducing the size of the magnesium-containing material and removing the magnetic fraction prior to carbonation.

17. milling the starting material to provide a particle size between 200 microns and 1000 microns to produce a sized material; removing the magnetic fraction from the sized material to produce a non-magnetic fraction; and grinding the non-magnetic fraction to produce a magnesium-containing material having a particle size of up to 75 microns; 20. The method of claim 16, further comprising:

18. The recycled CO ２ The by-product CO ２ The content of CO ２ The method according to any one of claims 1 to 17, wherein the concentration of the gas is at least 10% greater than that of the containing gas.

19. The recycled CO ２ The by-product CO ２ The content of CO ２ The method of claim 18, wherein the concentration of the gas is at least 20% greater than that of the containing gas.

20. The recycled CO ２ The by-product CO ２ The content of CO ２ 20. The method of claim 19, wherein the concentration of the gas is at least 50% greater than that of the containing gas.

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