EA043813B1 - OBTAINING LOW-CARBON MAGNESIUM OXIDE - Google Patents

Description

Field of technology

Generally, the technical field relates to the production of magnesium oxide from magnesium carbonates, more particularly to combining the production of magnesium oxide with the sequestration of carbon dioxide and the use of ultramafic rocks containing magnesium, such as serpentinite.

Prior Art

Magnesium oxide (MgO) is the most common base material used in the field of refractory materials. It is usually obtained by roasting magnesite (MgCO ₃ ) obtained from natural deposits, or by precipitation from saline solutions. By far, the firing method is the most used, despite the fact that it leads to various environmental problems.

The formation of CO2 during the decarbonization process that occurs during the production of magnesium oxide and the associated energy requirements are problematic. While energy efficiency and alternative sources can reduce CO2 emissions, more than 50% of process emissions come from the process itself.

Natural magnesite deposits on the planet are a large natural reservoir of CO2, permanently held and safely stored by natural geological processes occurring over millennia. Unfortunately, such substances are also the main source of MgO used in various industries, resulting in this CO2 being released back into the atmosphere and thus contributing to global warming.

There is a need for technologies that overcome at least some of the disadvantages of known processes for producing magnesium oxide.

Brief description of the invention

In some embodiments, a method for producing magnesium oxide is provided, comprising contacting CO ₂ -containing emissions with a magnesium-containing material to produce magnesium carbonate; subjecting magnesium carbonate to roasting to produce a by-product of CO2 and magnesium oxide; and reusing at least one portion of the CO2 byproduct to contact it with a magnesium-containing material to produce magnesium carbonate.

In some embodiments, the contacting step further includes obtaining a magnesium-containing material in an aqueous slurry and contacting the CO ₂ -containing emissions and CO ₂ byproduct with the aqueous slurry.

In some embodiments, the method includes: in the contacting step, providing a carbonate-rich slurry containing precipitable carbonates and substantially free of precipitated alkaline earth metal carbonates; separating the suspension saturated with carbonates into an aqueous phase containing precipitated carbonates and a solid phase; precipitation of magnesium carbonates from the aqueous phase; and separating magnesium carbonates from the aqueous phase.

In some embodiments, the CO ₂ -containing emissions include combustion gases from a magnesium oxide production plant.

In some embodiments, combustion gases are generated during the calcination step. Gaseous combustion products can be formed during the thermal activation stage of the magnesium-containing substance before being brought into contact with CO ₂ -containing emissions.

In some embodiments, the CO2 used to contact the magnesium-containing material is obtained solely from magnesium oxide production equipment.

In some embodiments, the CO ₂ -containing emissions comprise emissions from a separate emission source.

In some embodiments, the method includes thermally pre-activating the magnesium-containing material prior to contacting the CO ₂ -containing emissions.

In some embodiments, the thermal pre-activation is performed at a temperature of from about 600 to 700°C.

In some embodiments, the thermal pre-activation is performed for approximately 20-60 minutes.

In some embodiments, the CO2 produced from the thermal pre-activation is fed to the contacting step.

In some embodiments, the magnesium-containing material is contacted with a CO ₂ feed stream that includes a plurality of CO ₂ feed streams. The method may also include monitoring the relative amount of each CO ₂ feed stream in the CO ₂ feed stream. Control can be performed according to the pressure, temperature and/or composition of the CO2 feed streams.

In some embodiments, the CO2 feed stream further includes CO2 obtained from the additional magnesium oxide production line.

In some embodiments, the additional magnesium oxide production line includes a conventional production line.

In some embodiments, the magnesium-containing material includes serpentine or a material derived from serpentinite or variants thereof.

In some embodiments, the magnesium-containing material is derived from natural mines

- 1 043813 ral substances.

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

In some embodiments, the magnesium-containing material is pre-treated to form a magnesium-containing particulate prior to carbonation, and has a magnesium content of from about 1 to about 35 weight percent.

In some embodiments, the magnesium content is from about 10 to about 30 weight percent.

In some embodiments, the magnesium-containing substance is obtained from an industrial by-product. The industrial by-product may include steel slag and/or steel magnesium oxide waste brick.

In some embodiments, the magnesium-containing material is obtained from a mine residue. The mine residue may include residue from phyllosilicate mining and/or residue from chrysotile mining.

In some embodiments, the contacting step comprises contacting CO2 with a magnesium-containing material in substantially dry form in at least one carbonization unit at a carbonization temperature of about 200 to about 500°C and a carbonation pressure of about 1 to about 20 bar. to carbonize it to produce magnesium carbonates and CO2-depleted gas.

In some embodiments, the method includes reducing the size of the magnesium-containing material and removing the magnetic fraction prior to carbonation.

In some embodiments, the method includes grinding the starting material to provide a particle size of from about 200 to about 1000 microns to obtain a substance of a certain size; removing the magnetic fraction from a substance of a certain size to obtain a non-magnetic fraction; and grinding the non-magnetic fraction to obtain a magnesium-containing substance having a particle size of no more than 75 microns.

In some embodiments, the firing is carried out in an indirectly heated calciner. Firing can be carried out in a directly heated firing unit.

In some embodiments, the method includes monitoring at least one property of the CO ₂ -containing gas brought into contact with the magnesium-containing substance. Control may include adjusting the relative amounts of _CO2 -containing emissions and CO2 byproduct applied to contact with the magnesium-containing material. The control can be accomplished by controlling the gas pressure, gas temperature and/or CO2 content of the _CO2 -containing gas brought into contact with the magnesium-containing substance.

In some embodiments, the above-described method includes one or more features of any of the methods for producing magnesium carbonate as described in this invention.

In some embodiments, a method of producing magnesium oxide is provided, comprising: contacting a CO ₂ -containing gas with a magnesium-containing substance to produce magnesium carbonate; subjecting the magnesium carbonate to calcination to produce a by-product of CO ₂ and magnesium oxide; and reusing at least one portion of the CO ₂ byproduct as at least one portion of a CO ₂ -containing gas for contacting the magnesium-containing material to produce magnesium carbonate. Such a method may include one or more features as described above or later in this invention.

In some embodiments, a method of producing magnesium oxide is provided, comprising: bringing a CO ₂ -containing gas into contact with a magnesium-containing substance in an aqueous suspension; extracting precipitated magnesium carbonate from aqueous suspension; and subjecting the precipitated magnesium carbonate to calcination to produce a by-product of CO ₂ and magnesium oxide. Such a method may include one or more features as described above or later in this invention.

In some embodiments, the magnesium carbonate contains or consists of nesquegonite.

In some embodiments, a system for producing magnesium oxide is provided, including:

at least one carbonization plant having:

a gas supply for receiving CO ₂ -containing gas, a suspension supply for receiving an aqueous suspension containing a magnesium-containing substance, a carbonation vessel for carbonating at least one portion of magnesium in an aqueous suspension with CO2 to produce a CO2-depleted gas and a carbonate-rich suspension containing precipitates magnesium carbonates, a slurry outlet for removing carbonate-rich slurry containing precipitated magnesium carbonates, and a gas outlet for removing CO ₂ -depleted gas;

- 2 043813 separation unit having:

a slurry supply for receiving a carbonate-rich slurry containing precipitable magnesium carbonates from a slurry outlet of the at least one carbonation unit, a separation chamber for separating the carbonate-rich slurry containing precipitable magnesium carbonates into a solid phase and an aqueous phase containing precipitable magnesium carbonates, and a liquid outlet for removing the aqueous phase, and a sedimentation unit having:

supplying a suspension for receiving an aqueous phase, including precipitated magnesium carbonates, from a liquid outlet of the separation unit, a settling chamber for precipitating magnesium carbonates and forming a sedimentary suspension, and a liquid outlet for removing the sedimentary suspension;

a calcination unit for producing at least one batch of magnesium carbonates, producing a calcined magnesium oxide material and a CO2 by-product stream.

In some embodiments, the system includes a CO2 collection and supply system for collecting the CO2 byproduct stream for supply as at least one portion of CO2-containing gas to the carbonation unit.

In some embodiments, the system includes at least one additional feature of any of claims 1-39, or as described or illustrated in this invention.

Some embodiments provide the use of the residue from phyllosilicate mining to sequester carbon dioxide from industrial emissions and produce magnesium oxide.

Some embodiments provide the use of precipitated magnesium carbonate obtained from sequestering CO2 emissions with a magnesium-containing material to produce magnesium oxide by calcination.

Some embodiments provide the use of precipitated nesquegonite to produce magnesium oxide by calcination.

In some embodiments, the proposed method for producing magnesium oxide includes supplying magnesium carbonate consisting of precipitated nesquegonite to a calcination unit and calcining the precipitated nesquegonite to produce magnesium oxide.

In some embodiments, a magnesium oxide product is provided produced by calcining precipitated magnesium carbonate obtained by contacting a magnesium-containing material in wet or dry form with carbon dioxide from industrial emissions in a carbonation plant to form a carbonate-laden slurry and precipitate calcium or magnesium carbonate from the slurry. suspended carbonates in the sedimentation unit.

In some embodiments, the precipitated magnesium carbonate consists of nesquegonite.

In some embodiments, the method includes recovering a CO ₂ -containing calcination byproduct stream; and removing water from the CO ₂ -containing by-product to produce a treated CO ₂ by-product stream before contacting the treated CO ₂ by-product stream with the magnesium-containing material.

In some embodiments, the magnesium-containing material comprises evaporite.

In some embodiments, the evaporite is obtained from an evaporation plant.

In some embodiments, the evaporite contains a magnesium chloride salt.

In some embodiments, the evaporite contains a magnesium sulfide salt.

In some embodiments, the evaporite contains a magnesium carbonate salt.

In some embodiments, the evaporite is pre-treated prior to carbonation.

It should be noted that one or more features described above or later in this invention can be combined with methods, systems, applications and/or products as described above or later in this invention.

Brief description of graphic materials

Certain embodiments, aspects and embodiments of the technology are presented and will be further interpreted in conjunction with the following figures.

Fig. 1 is a flow diagram of a wet carbonization process.

Fig. 2 is a diagram of a carbonization plant.

Fig. 3 is a flow diagram of the wet carbonization process.

Fig. 4 is a diagram of the stages of a wet carbonization process with a reuse option.

Fig. 5 is a graph of the amount of dissolved magnesium versus temperature for wet carbonation for three different reaction times.

Fig. 6 is a graph of the amount of dissolved magnesium versus temperature for wet carbonation of an aqueous slurry with three different pulp densities.

Fig. 7 is a plot of CO2 removal versus gas/liquid ratio (GLR) for wet carbonation of aqueous slurry of different slurry densities.

- 3 043813

Fig. 8 is a graph of CO2 removal versus time for wet carbonation.

Fig. 9 is a graph of CO2 flow versus time for wet carbonation in continuous mode, showing the CO2 removal efficiency at 3.4 bar and 42 ml/min.

Fig. 10 is a response surface plot showing the mutual influence of temperature and pressure on the percentage of CO ₂ removal in direct gas/solid dry carbonation.

Fig. 11 is a graph of pressure versus time for gas/solid carbonation at 258° C. and 5.6 atm pressure. within 10 min.

Fig. 12 is a schematic diagram of a method for producing MgO.

Fig. 13 is a schematic diagram of a method for producing MgO and enabling capture of CO2 emissions from other industrial flue gas.

Fig. 14 is a flow diagram illustrating a two-train MgO production process that can be applied, for example, to a possible upgrade to an existing MgO production plant.

Although the invention will be described in conjunction with exemplary embodiments, it should be understood that these embodiments are not intended to limit the scope of the invention. Rather, they are intended to cover all alternatives, modifications and equivalents that may be included as defined by the appended claims.

Detailed Description of the Invention

This invention describes various methods for producing magnesium oxide and utilizing CO2 emissions and by-product streams.

In some embodiments, the methods facilitate the production of low carbon dioxide magnesium oxide from serpentinite through the carbonization of magnesium-containing materials, such as those derived from serpentinite.

Review of magnesium oxide production.

Regarding FIG. 12 and 13, they illustrate a general method for converting serpentinite to magnesium oxide. You can also use other magnesium-containing substances.

Serpentinite can be obtained from waste or residue, or extracted as ore. Carbonization of the serpentinite is carried out and may include one or more features as further described below, resulting in a relatively high quality magnesium carbonate stream, some examples of which may be referred to herein as nesquegonite, for use in the magnesium oxide production process. It should be noted that various forms of magnesite obtained from the carbonization of serpentinite or similar magnesium-containing substances can be used as raw materials for the production of magnesium oxide, including hydrated forms of magnesite such as dipingite (Mg ₅ (CO ₃ ) ₄ (OH) ₂ -5H ₂ O), hydromagnesite (Mg ₅ (CO ₃ ) ₄ (OH) ₂ -4H ₂ O), other hydrated forms of magnesium carbonate, and their combinations.

Nesquegonite or other magnesite substances produced by the carbonization process can be used as raw material to produce magnesium oxide by calcination. Roasting produces a CO2 by-product, which can be used in whole or in part to produce additional magnesite (eg nesquegonite) and then magnesium oxide.

The CO2 used in the carbonization step can be obtained from a separate industrial process, from a magnesium oxide production process as _CO2 -containing emissions (eg, from hydrocarbon combustion) and/or from at least one portion of the _CO2 by-product stream from the calcination step. . The carbonization step may be performed in a magnesium oxide production area, especially when the CO2 used for carbonation comes exclusively from the magnesium oxide production area. Alternatively, the carbonization step can be performed off-site at an industrial emission source, especially when the CO2 used for carbonation comes from the emission source.

The final magnesium oxide products can vary depending on the desired characteristics and production conditions, which can be obtained by adjusting firing parameters such as firing time and temperature.

Referring to FIG. 12, then in step 1 the serpentinite can be crushed and ground to achieve a particle size of approximately 200-1000, 300-700, 400-600 or approximately 500 microns. The magnetic fraction can then be removed by mechanical treatment(s). Various magnetic separation techniques can be used. The magnetic fraction mainly consists of hematite/magnetite/chromite and is a value-added product that can be further processed and sold. The non-magnetic fraction can be further reduced in size to produce a magnesium-containing dispersed substance having a particle size of no more than 75, no more than 50, no more than 40, or no more than 30 microns. The second size reduction stage improves the subsequent carbonation stage.

In stage 2, non-magnetic serpentinite is thermally activated. Thermal activation can be performed at a temperature of approximately 600-700°C for approximately 20-60 minutes. Emissions

- 4 043813

CO2 associated with thermal activation can be collected for use in stage 3.

The thermally activated serpentinite is then used as a feedstock for the carbonization step (Step 3). Here, thermally activated serpentinite is exposed to CO2 streams, which can be gas streams coming from both stage 2 and stage 4 in some embodiments. The composition of CO2 gas can vary, for example from 5 to 30%. Depending on the stage of the process (eg start-up, steady-state, shutdown, etc.), the CO2 content of the gas supplied to the carbonation unit may vary. For example, at startup, the _CO2 content may correspond to a combustion gas content of approximately 5 to 7%, for example, while during steady state processes, the CO2 content may correspond to a mixture of CO2 gas sources that includes both combustion gases and reused by-product gas CO2, and thus can be higher in the range of 25 to 30%. It should also be noted that in some embodiments the CO2 gas content may be much higher, for example in the range of 50 to 100%, if relatively pure CO2 is used, which may occur in certain embodiments which will be further discussed below.

Still looking at stage 3, the first by-product of stage 3 is an amorphous silicate phase that can be used as a filler. The second product of stage 3 is magnesium carbonate, which can be supplied for subsequent processing.

In step 4, the magnesium carbonate is calcined to produce magnesium oxide. In some embodiments, all CO ₂ byproduct emissions from the roasting are diverted to feed stage 3.

Referring now to FIG. 13, the production of low CO2 magnesium oxide can be associated with a CO2 capture plant at an industrial site. In this case, a second carbonation section (step 5) is added to the previously discussed option. By following this approach, magnesium oxide production can be increased and CO2 emissions from another industrial plant can be reduced.

In some embodiments, the method facilitates the production of low carbon magnesium oxide derived from magnesium-containing materials such as serpentine-based rocks (Mg ₃ Si ₂ O ₅ (OH) ₄ ). CO ₂ is converted into carbonates when interacting with magnesium contained in the structure of the mineral. According to recent research, a serpentinite process has been developed for treating industrial flue gas, economically helping to reduce CO ₂ emissions, as well as producing nesquegonite with a very high degree of purity. In turn, such nesquegonite can be used as a raw material for further processing in order to profitably obtain magnesium oxide by roasting. In addition, both serpentinite carbonization and magnesite decarbonization can be performed in the same industrial unit to offset the CO2 emissions resulting from magnesite calcination. The result is a method of producing magnesium oxide where the CO2 is reused in a cyclic process and is not released into the atmosphere, resulting in a low carbon footprint and a high purity magnesium oxide product.

In one aspect, the methods described in this invention can facilitate the production of magnesium oxide without large emissions of CO2 into the atmosphere by using a natural deposit of magnesite as a raw material.

In another aspect, the methods described in this invention can facilitate the inclusion of CO ₂ emissions from calcination of magnesite to produce more magnesium oxide from carbonation of serpentinite. In another aspect, the methods described in this invention can facilitate the production of magnesium oxide from magnesite that has been produced by carbonization of serpentinite using industrial CO ₂ generated at another industrial site.

Referring to FIG. 14, it should be noted that the equipment for producing magnesium oxide may include two or more processing lines, each of which produces an output stream of MgO. In fig. 14 shows two lines, one of which is a conventional line into which magnesite from natural deposits is supplied for calcination, and the second line, which may be new or modified, as illustrated, includes serpentine or the like as a carbonation-precipitation raw material, and the resulting MgCO ₃ is fed to calcination, producing a serpentine derivative of MgO. Various CO2 streams are generated in this multi-train process and it should be noted that one or more _CO2 streams may be used in the carbonation step.

CO2 streams can be collected using a CO2 collection system, which may include pipes, compressors (if necessary depending on pressure conditions), vessels, valves, condensers, particle filters, heat exchanger(s) for heating or cooling the gas and/or control device. Depending on the availability and properties (eg pressure, temperature, CO2 content) of the different CO2-containing streams, the collection system and the CO2 inlet to the carbonation plant can be adjusted. The CO2 collection and supply system can also be a relatively simple assembly that seamlessly connects the roaster gas outlet to the carbonation unit gas inlet.

In some embodiments, the CO ₂ -containing gas is directly supplied to the carbonization unit without any significant intermediate installations; in such embodiments, operating conditions may be provided in the roasting and carbonization plants to facilitate direct CO ₂ supply between the two plants. In addition, when there is an excess of possible CO ₂ , there may be installations for storage

- 5 043813 facilities that retain CO2 from one or more selected sources.

The CO2 collection and supply system can have various configurations.

In some embodiments, the CO2 collection and supply system is gas-tight to prevent CO2 leaks. The CO2 collection and supply system may include collection lines hydraulically coupled to the calcination unit and a CO2 supply line hydraulically coupled to the carbonation unit. In addition, there may be one or more compressors and/or heat exchangers as part of the CO ₂ collection and supply system to supply the CO ₂ to the carbonization unit at the required temperatures and pressures.

In some embodiments, the calciner is either a direct fired calciner or an indirect fired calciner. In direct fired calcination, the resulting CO ₂ -containing by-product stream is a gas mixture stream that includes CO 2 from both magnesite decarbonization and fuel combustion, as well as other gas components. The CO2 by-product stream from a direct fired calciner may have a CO2 content higher than the combustion emissions and thus may be preferable to CO2 emissions for supply to the carbonization unit. In indirect roasting, the _CO2 -containing by-product stream is predominantly CO2 from the decarbonization of magnesite, and due to its high CO2 content of up to 100%, it may be preferable to other CO2 streams (e.g. CO2 emissions, CO2-containing by-product stream from direct fired roasting from another line, etc.) to feed into the carbonization unit to provide greater driving force for carbonation reactions and smaller equipment size (eg vessel, pipes, etc.).

Moreover, the CO ₂ -containing stream that is used in the carbonation unit can be selected based on higher pressures to activate the carbonation reaction. CO2 streams from combustion emission sources may have relatively low pressures, while the CO2 stream from roasting may have higher pressures and thus may be selectively used for the carbonation step. For example, as the process transitions from start-up to normal operation, increasing amounts of CO ₂ from roasting can be used for carbonation.

In some embodiments, the magnesium carbonate feedstock that is fed to the calcination consists of nesquegonite that has been produced according to the carbonation-precipitation process described in this invention. By providing nesquegonite having a predetermined state of hydration for firing, control and processing during the firing step can be improved. For example, when feeding nesquegonite for firing, heating can be predetermined based on the known state of hydration of the nesquegonite, whereas magnesium carbonate obtained from natural deposits may contain a complex mixture of hydrated substances for which it is difficult to reliably determine the enthalpy of dehydration.

Possible methods of CO2 binding when producing magnesium carbonate and combining to produce magnesia.

Various possible methods can be used in combination with the above-described embodiments of producing magnesium oxide to sequester carbon dioxide and produce alkaline earth metal carbonates for use in producing magnesium oxide.

In one aspect, in combination with a method for producing MgO, a method is provided for chemically sequestering carbon dioxide from a gas containing carbon dioxide by producing alkaline earth metal carbonates. The carbon dioxide-containing gas can be obtained from industrial emissions, and it has different concentrations of carbon dioxide according to the production process from which the emissions are obtained.

In some possible aspects, in combination with a method for producing MgO, a method is provided for chemically sequestering carbon dioxide from industrial emissions that contain carbon dioxide during carbonation using magnesium or calcium silicate, preferably magnesium silicate, or other magnesium-containing substances that are a source of magnesium. In some aspects, a similar process can be implemented to produce CaO using chemical sequestration of carbon dioxide from industrial emissions that contain carbon dioxide during carbonation of calcium-containing substances.

Most of the research up to this point has been carried out using gases containing 100% CO2, meaning that carbon dioxide from the stack of industrial equipment must first be concentrated using separate technologies before it is carbonized. This means a more expensive method. In 2011, a carbon capture and sequestration (CCS) pilot plant opened at a coal burning plant in the United Kingdom. Experts have found that between 16 and 40% of the energy generated could ultimately be used for carbon capture and storage. This equates to a $100 million installation producing electricity costing between $16 million and $40 million.

Embodiments of the present invention may allow for increased economic efficiency by providing profits or costs from zero to 10% of the cost of energy produced.

- 6 043813

In some possible aspects, the carbon dioxide-containing gas may advantageously be gas emissions that are used as soon as they are received from the installation. For example, for a cement plant, a gas containing 18.2% CO ₂ , 4.11% O ₂ and 77.69% N ₂ can be used. The optional carbon dioxide-containing gas derived from industrial emissions may have a carbon dioxide concentration of from about 1 to about 30%.

Embodiments of the present invention may also allow the production of valuable alkaline earth metal carbonates from the alkaline earth metal containing material.

It should be understood that the alkaline earth metal containing substance may be a naturally occurring substance, which may include, but is not limited to, alkaline earth metal containing minerals and alkaline earth metal containing rocks. For example, the alkaline earth metal containing material may include serpentine or serpentinite. Optionally, the alkaline earth metal containing material may include alkaline earth metal containing rocks such as sandstone, granite, anorthosite, basalt, serpentinite, peridotite, serpentized peridotite, ophiolitic rocks, mafic and ultramafic rocks (containing Mg and Fe minerals), rocks containing more than 10% pyroxene and peridot, or a combination of both. Optionally, the alkaline earth metal containing substance may also include phyllosilicate. Additionally, the optional alkaline earth metal containing material may 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 group containing antigorite, chrysotile, lizardite), wollastonite, calcium oxide (CaO), magnesium oxide or periclase (MgO), brucite (Mg(OH) ₂ ), mafic and ultramafic minerals (containing Mg and Fe), or a combination of them.

In some embodiments, the magnesium-containing material that is used as a raw material may include magnesium-containing evaporite. Evaporite is a sedimentary deposit of precipitated minerals formed by the evaporation of an aqueous solution. In some cases, evaporitic materials may contain elevated concentrations of magnesium. Evaporite may include a magnesium-containing particulate matter that is relatively reactive due in part to its small particle size. Evaporite can be produced in evaporation plants used in various industries. On the other hand, evaporite can be obtained from natural rocks formed by the evaporation of former seas or salt lakes. Evaporites may include magnesium in the form of various magnesium salts of chlorides, sulfates and/or carbonates, such as carnallite (KMgCl ₃ -6H ₂ O), kainite (KMg(SO ₄ )Cl-3H ₂ O), kieserite (MgSO ₄ -H ₂ O), langbeinite (K ₂ Mg ₂ (SO ₄ ) ₃ ), polyhalite (K ₂ Ca ₂ Mg (SO ₄ ) ₆ -H ₂ O) and magnesite (MgCO ₃ ). Depending on the chemical nature and physical structure of the evaporitic material, it can be pre-treated using thermal and/or chemical steps to form a pre-treated magnesium-containing material for use in the carbonation step.

The alkaline earth metal containing substance can also be obtained from various industrial wastes or residues, such as slag, cement waste, mining waste and mineral processing waste, which are available without the need for extraction from geological formations. Optionally, the slag may include steel slag, MgO steel waste brick, or a combination thereof. Optionally, cement waste may include dust from a rotary kiln (CKD, cement kiln dust, LKD, lime kiln dust), defective cement, defective concrete, construction and dismantling waste, concrete with aggregates, concrete stone, concrete, red brick or a combination of these. Optionally, waste from mining and mineral processing may include residue from phyllosilicate mining, residue from chrysotile mining, serpentine (as in the matrix of a rock containing an ore), or a combination thereof.

Referring to FIG. 1, in some embodiments, the method includes the step of supplying a carbon dioxide-containing gas 2 and an aqueous slurry 4 comprising an alkaline earth metal-containing material 6 and water 8 to a carbonization unit 10. The carbonization unit 10 may include a gas supply 12 to receive the gas. 2 containing carbon dioxide, and supplying a slurry 14 to receive the aqueous slurry 4. The method then includes the step of contacting the gas 2 containing carbon dioxide with the aqueous slurry 4 in a carbonization unit 10 to carbonize at least one portion of the alkaline earth metal. A gas 16 depleted in carbon dioxide and a suspension 18 partially saturated with carbonates, containing precipitated carbonates, are obtained. The method may also include the step of removing carbon dioxide-depleted gas 16 from carbonation unit 10 via gas vent 17 and carbonate-laden slurry 18 via slurry bleed 19. In some embodiments, the carbonate-laden slurry contains substantially unprecipitated carbonates and is removed from carbonation units 10. The carbonate-saturated slurry 18 is then separated in a separation unit 20 into a solid phase 24 and an aqueous phase 28 containing precipitated carbonates, which are respectively removed from the separation unit 20 through a solids outlet 26

- 7 043813 and liquid outlet 30. In some embodiments, the aqueous phase 28 contains substantially non-precipitated carbonates and is removed as is from the separation unit 20. The aqueous phase 28 can then be supplied to the precipitation unit 32 via a liquid inlet 33. The method may include precipitation of at least one portion of the precipitable carbonates of the aqueous phase 28 in the form of alkaline earth metal carbonates in the precipitation unit 32, thereby forming a sediment slurry 38 including alkaline earth metal carbonates, which is removed from the precipitation unit 32 through the suspension outlet 40.

It should be understood that the aqueous slurry 4 containing the alkaline earth metal containing substance 6 may be formed before being supplied to the carbonization unit 10, as shown in FIG. 2, but may also be formed directly in the carbonization unit 10 during the separate supply of the alkaline earth metal containing substance 6 and water 8 to the carbonization unit 10.

In some possible aspects, the method may further include the step of mixing the aqueous slurry in the carbonization unit to increase contact between the carbon dioxide-containing gas and the alkaline earth metal-containing substance. Mixing can be provided by a mixing device, such as a stirrer, having a rotation speed of from about 400 to about 800 rpm, optionally from about 500 to about 650 rpm. It should be understood that the mixing step is not limited to mechanical mixing and may include various known and suitable mixing methods, such as gas fluidization.

In some possible aspects, the method may also include agitating the aqueous phase in the precipitation unit to enhance precipitation of alkaline earth metal carbonates.

In some possible aspects, the alkaline earth metal-containing material may be mixed with water to form an aqueous slurry having a slurry density (also referred to as the mass concentration of total solids per liter of slurry) from 25 to 300 g/L. The low density of the pulp may promote the dissolution of the alkaline earth metal in the aqueous suspension. The effect of the density of suspended water on the efficiency of carbon dioxide removal is shown in example 2.

In some possible aspects, the method may include thermally pre-treating the alkaline earth metal-containing material to perform dehydroxylation. Indeed, the alkaline earth metal containing material may indeed include unwanted water, which is at least partially removed by thermal pretreatment. During thermal pretreatment, the water evaporates and the crystalline structure of the alkaline earth metal-containing substance can be changed to a more reactive structure, allowing the alkaline earth metal to be better dissolved in the aqueous phase. Optionally, the method may include heating the alkaline earth metal containing material at a pretreatment temperature of from about 500 to about 800°C for a pretreatment time of from about 10 to about 60 minutes. Optionally, the pretreatment temperature can be from about 600 to about 700°C, and the pretreatment time can be from about 15 to about 40 minutes. Optionally, the pretreatment temperature may be low enough to avoid recrystallization of the alkaline earth metal containing material. The effect of thermal pretreatment on carbon dioxide removal efficiency is shown in Example 3.

In some possible aspects, the method may 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 promote carbonation of the alkaline earth metal. Optionally, the alkaline earth metal-containing material can be crushed and/or ground such that the average particle size of the material is from about 10 to about 45 microns, and such that at least about 90% of the solid particles are from about 0 to about 45 microns. 75 microns. Optionally, the crushing and/or grinding step can be performed before the thermal pretreatment step, since dehydroxylation may be facilitated by the use of reduced particle size of the material.

Referring to FIG. 3, the method may include crushing and/or grinding the alkaline earth metal containing substance 6 in a crushing/grinding unit 42 to reduce the particle size of the alkaline earth metal containing substance. The crushed and/or ground substance 6 is then fed to a thermal pretreatment unit 44 to dehydroxylate it as mentioned above. Water 8 and pretreated material 6 may be supplied to the carbonation unit 10 separately to form an aqueous slurry within the carbonation unit 10 to contact the feed gas 2 containing carbon dioxide to form an aqueous slurry 18 containing precipitated carbonates and gas 16 , depleted of carbon dioxide. The aqueous slurry 18 is fed to a separation unit 20 to separate it into an aqueous phase 28 containing precipitated carbonates and a solid phase 24. At least one portion 25 of the solid phase 24 can be reused as at least one portion of the alkaline earth metal substance 6 in draw

- 8 043813 beating/grinding unit 42. At least a portion of the aqueous phase 28 containing precipitable carbonates is supplied to a precipitation unit 32 to precipitate alkaline earth metal carbonates and produce a sediment slurry 38. The sediment slurry 38 can be fed to a second separation unit 46 for separation into an alkaline earth metal carbonate stream 50 and a liquid stream 48. At least one portion of the liquid stream 48 may be reused as at least one portion of water 8 in the carbonation unit 10.

In some possible aspects, the step of precipitation of alkaline earth metal carbonates can be performed at a precipitation temperature of from about 20 to about 80°C, and a precipitation time from about 0.5 to about 12 hours with or without stirring.

In some possible aspects, the alkaline earth metal carbonate precipitates produced by the present process are between 90 and 99.9% pure.

In some possible aspects, the carbon dioxide-containing gas can be continuously supplied to the carbonization unit while maintaining a certain or desired carbon dioxide removal efficiency (see Example 5). Optionally, the process can be controlled in accordance with a number of batch processes, including reverse flows to increase the rate of carbonation of solids (see example 6). For example, a variant of the recycling process may be carried out such that the same portion of an alkaline earth metal-containing substance is contacted with multiple portions of a gas containing carbon dioxide before precipitating as alkaline earth metal carbonates.

In some possible aspects, the method may include reusing the solids separated from the carbonate-laden slurry to produce a new batch of aqueous slurry for contact with a gas containing carbon dioxide in a carbonation unit. It should be noted that reuse may also be referred to as recycling in this invention.

Fig. 4 shows a process flow diagram with various steps associated with recycling various liquid and solid streams according to possible embodiments of the present invention. The plurality of streams may indeed be reused in the carbonation unit, with gas containing carbon dioxide being supplied continuously or batchwise to the carbonation unit.

Gas supply in periodic mode.

In some possible aspects, the gas containing carbon dioxide can be supplied to the carbonization unit in portions of the gas containing carbon dioxide.

Stage 1.

A first portion of gas containing carbon dioxide, called gas 1, is brought into contact in a carbonization unit for a certain time with an aqueous slurry resulting from the combination of solid 1 and liquid. For example, the aqueous slurry may have a mass concentration of the alkaline earth metal containing material of 150 g/L, and the aqueous slurry may be contacted with each portion of the carbon dioxide containing gas for 30 minutes.

After each 30-minute contacting step, the resulting carbonate-rich slurry is separated into a solid phase and an aqueous phase. It should be noted that the first gas portion, gas 1, may be represented as two sub portions, for example to satisfy pressure constraints. Therefore, two sub-portions of gas, each of which is in contact with the solid for 15 minutes, can be supplied to the carbonation unit sequentially.

The mass balance between the carbon dioxide containing gas and the carbon dioxide depleted gas indicated that a maximum of 5.91 g CO ₂ /L gas (1.64 g C/L gas) was processed after each 30 minute contacting step.

Stage 2.

The aqueous phase is then fed to a precipitation unit and, after sufficient alkaline earth metal carbonates have precipitated, the slurry is separated into a solids stream and an aqueous stream.

Stage 3.

The aqueous stream is then reused as a liquid in the carbonization unit.

The above three steps 1-3 are repeated two more times to contact the second and third gases containing carbon dioxide, called gas 2 and gas 3.

After being brought into contact with gas 2 and gas 3, solid 1 is dried, ground and heated in a pre-treatment unit as previously described.

Steps 1-3 are performed three more times with the crushed and heated solid phase, solid 1 is brought into contact sequentially with gas 4, gas 5 and gas 6. After being brought into contact with six portions of gas containing carbon dioxide (gas 1 to gas 6 ) the solid phase reaches the limits of its reactivity.

All of the above described stages of the method can then be repeated with a new portion of the substance containing the alkaline earth metal.

Continuous gas supply.

- 9 043813

In some other possible aspects, a stream of gas containing carbon dioxide may be supplied continuously to the carbonization unit. In the periodic mode, the controlled key parameter was the contact time of a portion of gas containing carbon dioxide. On the other hand, in continuous mode, the key parameter controlled is the amount of dissolved carbon dioxide in the water suspension.

According to the above batch process example, a maximum of 5.91 g CO ₂ /L gas (1.64 g C/L gas) is treated after each 30-minute contacting step. Taking into account that all carbon dioxide treated is dissolved in aqueous suspension, the maximum concentration of dissolved carbon dioxide should not exceed approximately 5.0 g C/l. At values higher than this, precipitation may occur inside the reactor.

Therefore, in continuous operation, after the dissolved carbon dioxide concentration of 5.0 g C/L in the aqueous slurry is measured, the aqueous slurry is removed from the carbonation unit and separated into a solid phase and an aqueous phase. The aqueous phase is then fed into the precipitation unit.

Optionally, depending on the rate of precipitation of the alkaline earth metal carbonates in the precipitation unit, a certain volume of water may be supplied to the aqueous phase to maintain a low concentration of dissolved carbon dioxide in the recirculated aqueous phase as the steps progress.

For example, after the total amount of carbon dioxide processed reaches 16.04 g CO ₂ /L gas (4.4 g C/L gas), the separated solids can be dried, crushed and heated before further reuse.

Therefore, steps 1-3 can be performed again sequentially, following the same option as described above, to achieve a total amount of carbon dioxide processed of approximately 27.28 g CO ₂ /L gas (7.47 g C/L gas) for the total batch of three stages 1-3. Then, a new batch of the alkaline earth metal containing solid can be used.

It should be understood that any of the above aspects of each method, method, system, application and substance can be combined with any other aspect, unless the two aspects clearly cannot be combined due to their mutual exclusivity. For example, the various operating steps of the methods described in this invention above, in this invention below and/or in the accompanying figures can be combined with any method, system or application descriptions found in this invention and/or according to the accompanying claims.

It should also be understood that various parameter values obtained and/or described in any of the examples, tables and description in this invention may be considered as maximum, minimum or intermediate values, and that various ranges may be obtained from these maximum, minimum or intermediate values. meanings as described in this invention or in the accompanying figures and claims.

In some embodiments, a method for producing MgO includes a preceding method for producing magnesium carbonate and sequestering carbon dioxide from a gas containing carbon dioxide. The method may include: contacting a carbon dioxide-containing gas with an aqueous slurry containing an alkaline earth metal-containing substance in a carbonization unit to carbonate at least one portion of the alkaline earth metal to produce a carbon dioxide-depleted gas and a carbonate-rich slurry, comprising precipitable carbonates and substantially free of precipitated alkaline earth metal carbonates; removing the carbonate-laden slurry from the carbonation unit and separating the carbonate-laden slurry into an aqueous phase containing carbonates and a solid phase; and supplying the aqueous phase to the precipitation apparatus and precipitating the alkaline earth metal carbonates in the precipitation apparatus to produce a sediment slurry.

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

In some embodiments, the method may further include the step of mixing the aqueous slurry containing the alkaline earth metal-containing substance in the contacting step in the carbonization unit. Optionally, the method may also include the step of mixing the aqueous phase during the precipitation step of alkaline earth metal carbonates in a precipitation unit.

In some embodiments, the method may further include the step of mixing the alkaline earth metal containing substance with water prior to the contacting step to dissolve the alkaline earth metal ions in the aqueous phase and form an aqueous slurry.

In some embodiments, the method may further include a step of mixing the alkaline earth metal containing substance with water concurrently with the contacting step to dissolve the alkaline earth metal ions in the aqueous phase and form an aqueous slurry within the carbonization unit.

Optionally, the mixing step can be performed such that an aqueous slurry is formed having a mass concentration of from 25 to 300 g/l in grams of total solids per liter of aqueous slurry.

In some embodiments, the method may further include separation of sediments

- 10 043813 suspension on a solids stream containing carbonates of alkaline earth metals and an aqueous stream.

In some embodiments, the method may further include drying the solids stream containing alkaline earth metal carbonates.

In some embodiments, the method may further include reusing at least one portion of the aqueous stream in the carbonation unit.

In some embodiments, the method may further include reusing at least one portion of the solid phase in the carbonization unit as at least one portion of the alkaline earth metal-containing material to contact the carbon dioxide-containing gas.

In some embodiments, the method may further include thermally pretreating the alkaline earth metal containing substance to dehydroxylate it to produce a pretreated alkaline earth metal containing substance for contact with a gas containing carbon dioxide. Optionally, the thermal pretreatment step of the alkaline earth metal containing substance may include heating the alkaline earth metal containing substance at a temperature of from about 500 to about 800° C. during the pretreatment of about 10 to about 60 minutes. Optionally, the temperature can be from about 600 to about 700°C, and the pretreatment time can be from about 15 to about 40 minutes.

In some embodiments, the method may further include crushing and/or grinding the alkaline earth metal-containing substance prior to contacting the carbon dioxide-containing gas. Optionally, the crushing and/or grinding step can be performed prior to the thermal pretreatment step of the alkaline earth metal containing substance. Additionally, an optional crushing and/or grinding step can be performed to obtain solid particles having a median size of from about 10 to about 45 microns, and thus to obtain 90% of the solid particles having a size from about 0 to about 75 microns.

In some embodiments, the carbon dioxide containing gas may be derived from industrial emissions and may have a carbon dioxide concentration of 1 to 30%.

In some embodiments, the method may further include controlling at least either the carbonation temperature, the stirring rate, or the carbonation pressure in the carbonation unit.

Optionally, the contacting step in the carbonization unit can be performed at a carbonation temperature of from about 10 to about 40°C. Optionally, the carbonation temperature can be from about 20 to about 30°C.

Optionally, the contacting step in the carbonization unit can be performed at a carbonization pressure of from about 1 to about 20 bar. Optionally, the carbonation pressure can be from about 2 to about 12 bar.

Optionally, the stirring speed in the carbonation unit can be from about 400 to about 800 rpm, and optionally from about 500 to about 650 rpm.

In some embodiments, the deposition step can be performed at a deposition temperature of from about 20 to about 80°C for a deposition time of from about 0.5 to about 12 hours. Optionally, the precipitation step may include stirring the aqueous phase.

In some embodiments, the alkaline earth metal containing material may include at least one of: sandstone, granite, anorthosite, basalt, serpentinite, peridotite, serpentized peridotite, ophiolitic rocks, mafic and ultramafic rocks, rocks containing more than 10% pyroxene and peridot , calcium silicate, magnesium silicate, feldspar, plagioclase feldspar, peridot, pyroxene, olivine, serpentine, wollastonite, calcium oxide, magnesium oxide, brucite, mafic and ultramafic minerals, steel slag, steel waste brick MgO, rotary kiln dust ( CKD, LKD), defective cement, defective concrete, construction and dismantling waste, concrete with aggregates, concrete stone, concrete, red brick, residue from phyllosilicate mining and/or residue from chrysotile mining.

In some embodiments, the alkaline earth metal may include calcium or magnesium.

In some embodiments, the method may further include continuously supplying a gas containing carbon dioxide to the carbonization unit. Optionally, the method may include monitoring or adjusting the maximum amount of dissolved carbon dioxide in the carbonate-laden slurry produced in the carbonation unit, the maximum amount of dissolved carbon dioxide being selected to reduce or prevent precipitation of alkaline earth metal carbonates in the carbonation unit. Optional maximum number

- 11 043813 in dissolved carbon dioxide may be no more than 5 g/l.

In some embodiments, the carbon dioxide containing gas may include multiple portions of the carbon dioxide containing gas, the method comprising: supplying at least one portion of the carbon dioxide containing gas to a carbonization unit; contacting the aqueous slurry with at least one portion of a gas containing carbon dioxide in a carbonization unit to produce a carbonate-rich slurry; removing the carbonate-laden slurry from the carbonation unit and separating the carbonate-laden slurry into an aqueous phase containing precipitated carbonates and a solid phase; and reusing the solid phase in the carbonation unit and supplying water to the carbonation unit to form a new portion of the aqueous slurry; bringing a new portion of an aqueous suspension into contact with another portion of a gas containing carbon dioxide to produce a suspension saturated with carbonates.

In some embodiments, the carbon dioxide-containing gas may be supplied to the carbonization unit in the form of multiple portions of carbon dioxide-containing gas, the method comprising: contacting the aqueous slurry with at least one portion of the carbon dioxide-containing gas in the carbonization unit to obtain suspension saturated with carbonates; removing the carbonate-laden slurry from the carbonation unit and separating the carbonate-laden slurry into an aqueous phase containing precipitated carbonates and a solid phase; and supplying an aqueous phase containing precipitable carbonates to a precipitation unit, precipitating alkaline earth metal carbonates in the precipitation unit to produce a sediment slurry, and separating the sediment slurry into a solids stream containing the alkaline earth metal carbonates and an aqueous stream; reusing the solids and water stream in the carbonization unit to produce a new batch of aqueous slurry, and bringing the new batch of aqueous slurry into contact with another batch of gas containing carbon dioxide to produce a carbonate-rich slurry.

Optionally, the method may include supplying water to the carbonization unit as an additional stream of a new portion of the aqueous suspension.

In some embodiments, the contacting step in the carbonation unit may be performed during a maximum gas contact time, the maximum gas contact time is controlled or adjusted to reduce or prevent precipitation of alkaline earth metal carbonates in the carbonation unit. Optionally, the maximum gas contact time can be from about 1 to about 60 minutes.

In some embodiments, the method may also include crushing and/or grinding the solid phase prior to reuse in the carbonization unit to produce a new batch of aqueous slurry.

In some embodiments, a method for sequestering carbon dioxide from a gas containing carbon dioxide is provided. The method includes: bringing a gas containing carbon dioxide into contact with an aqueous slurry containing a magnesium-containing substance in a carbonation unit at a carbonation temperature of from about 10 to about 40°C and a carbonation pressure from about 1 to about 20 bar, to carbonate at least at least one portion of magnesium to produce a carbon dioxide-depleted gas and a carbonate-rich slurry containing precipitated carbonates and substantially free of precipitated magnesium carbonates.

In some embodiments, the method may include: removing the carbonate-laden slurry from the carbonation unit and separating the carbonate-laden slurry into a solid phase and an aqueous phase including precipitable carbonates and substantially free of precipitated magnesium carbonates; and supplying the aqueous phase to the precipitation apparatus and precipitating the magnesium carbonates in the precipitation apparatus to produce a slurry including precipitated magnesium carbonates.

In some embodiments, the method may further include separating the slurry into a solids stream containing precipitated magnesium carbonates and an aqueous stream.

In some embodiments, a method of sequestering carbon dioxide from a gas containing carbon dioxide is provided, wherein the gas containing carbon dioxide is contacted with an alkaline earth metal containing substance in substantially dry form in at least one carbonization unit at a carbonization temperature from about 200 to about 500°C and a carbonization pressure from about 1 to about 20 bar to carbonate it into carbonates and carbon dioxide-depleted gas.

In some embodiments, a method of sequestering carbon dioxide from industrial emissions is provided wherein the industrial emissions are contacted with magnesium silicate material in wet or dry form to produce a gas depleted of carbon dioxide and carbonated magnesium silicate material.

In some embodiments, a method for making alkaline earth metal carbonates is provided, comprising: a contacting step in which industrial emissions containing carbon dioxide are brought into contact with an aqueous slurry containing an alkaline earth metal containing substance to produce a carbon dioxide-depleted gas, and a stream alkaline earth metal carbonates substantially free of precipitated alkaline earth carbonates

- 12 043813 metals; a precipitation step in which alkaline earth metal carbonates are precipitated from the alkaline earth metal carbonate stream, thereby obtaining a sediment slurry; and a separation step in which the sediment suspension is separated into precipitated alkaline earth metal carbonates and an aqueous phase.

In some embodiments, a method for making alkaline earth metal carbonates is provided, comprising: a contacting step in which industrial emissions containing carbon dioxide are brought into contact with an aqueous slurry containing an alkaline earth metal containing substance to produce a carbon dioxide-depleted gas, and a stream alkaline earth metal carbonates containing precipitated carbonates and substantially free of precipitated alkaline earth metal carbonates; a first separation step in which the alkaline earth metal carbonate stream is separated into a solid phase and an aqueous phase containing precipitated carbonates and substantially free of precipitated alkaline earth carbonates; a reuse step in which the solid phase is reused in the carbonization step as at least one portion of an alkaline earth metal containing substance; a precipitation step in which alkaline earth metal carbonates are precipitated from the aqueous phase, thereby obtaining a sediment slurry containing precipitated alkaline earth metal carbonates; and a separation step in which the sediment suspension is separated into precipitated alkaline earth metal carbonates and an aqueous phase.

In some embodiments, a carbon dioxide sequestration system is provided for sequestering carbon dioxide from a gas containing carbon dioxide. The system includes: at least one carbonization unit having: a gas supply for receiving gas containing carbon dioxide, a suspension supply for receiving an aqueous suspension containing a substance containing an alkaline earth metal, a carbonization vessel for carbonizing at least one portion of the alkaline earth metal of the aqueous suspension with carbon dioxide to produce a carbon dioxide-depleted gas and a carbonate-rich slurry containing precipitable carbonates and substantially free of precipitated alkaline earth carbonates, a slurry vent for removing a carbonate-rich slurry containing precipitable carbonates, and a gas vent for removing the dioxide-depleted gas carbon, a separation unit having: a suspension supply for receiving a suspension saturated with carbonates containing precipitable carbonates from a suspension outlet of at least one carbonization unit, a separation chamber for separating the suspension saturated with carbonates containing precipitable carbonates into a solid phase and an aqueous phase containing precipitable carbonates and substantially free of precipitated alkaline earth metal carbonates, liquid withdrawal for aqueous phase removal, and solids removal for solid phase removal; and a sedimentation unit having: a suspension supply for receiving an aqueous phase containing precipitated carbonates from a liquid outlet of the separation unit, a settling chamber for precipitation of alkaline earth metal carbonates and formation of a sedimentary suspension, and a liquid outlet for removing the sedimentary suspension.

Some embodiments provide the use of a magnesium-containing material in the form of an aqueous slurry to contact and bind carbon dioxide from a gas containing carbon dioxide at a temperature of about 20 to about 30°C and a pressure of about 2 to about 12 bar to form magnesium carbonates .

Some embodiments provide the use of the residue from phyllosilicate mining to sequester carbon dioxide from industrial emissions and produce magnesium carbonates. Optionally, the phyllosilicate mining residue includes at least one of lizardite, antigorite, brucite, iron oxide, chromium oxide and chrysotile.

In some embodiments, a precipitated calcium or magnesium carbonate (PCC or PCM) is provided by contacting a calcium or magnesium containing substance in wet form with carbon dioxide from industrial emissions in a carbonation plant to form a carbonate-laden slurry, and precipitating calcium or magnesium carbonate from carbonate-saturated suspension in a sedimentation unit.

In some embodiments, a precipitated calcium or magnesium carbonate (PCC or PCM) is provided containing at least 95 wt.% calcium or magnesium carbonate in dry form or hydrated form.

It is also observed that a higher CO ₂ content in the calcination exhaust gas is advantageous for the carbonation reaction and will increase the efficiency of the overall process. The firing can be adjusted to produce a higher CO2 content in some cases, such as when the firing unit is operated under certain operating conditions and using certain reagents. For example, in some embodiments, the calciner can be adjusted to increase the CO2 concentration in the emissions to ensure complete combustion of the natural gas or other fuel used, which may include introducing excess preheated air to promote complete combustion and reduce fuel consumption. The air flow rate can be controlled in this way and the calciner can be suitably closed to minimize the introduction of other gases that could dilute the system. In addition, we must

- 13 043813 The calcination tank can be adjusted to increase the oxygen content in the gas supply, thereby reducing the concentration of other gas components that may be in the air. The oxygen level may be provided and/or the calciner may be otherwise adjusted such that the resulting emissions have a CO2 content higher than the CO2 content of the flue gas fed to the carbonization plant. Thus, recycling CO2 from roasting back into the carbonation stage can increase the CO2 concentration and thereby improve overall efficiency. In some examples, the CO2 concentration in the recycle emissions may be at least 1, 2, 5, 10, 15, 20, 25, 30, 40, or 50% greater than the CO2 concentration in the flue gas.

In some embodiments, the method includes contacting a CO ₂ -containing stream with a magnesium-containing material to produce magnesium carbonate; roasting magnesium carbonate to produce a CO ₂ -containing gas by-product and magnesia, the CO ₂ -containing gas by-product having a higher CO 2 concentration than the CO ₂ -containing stream; and reusing at least one portion of the CO ₂ -containing gas byproduct to contact the magnesium-containing material to produce magnesium carbonate. The CO ₂ -containing stream may be from a first emission source and may be a flue gas (eg, from a power plant or other source). The CO ₂ -containing stream may, for example, have a CO 2 content of from 10 to 20 wt.%. The CO ₂ -containing gas byproduct may have a higher CO ₂ content, which may be several percentage points higher (for example, 12 to 22 wt.% CO2) or may be significantly higher (for example, 30, 40, 50 wt.% CO2). % or even close to 100 wt.% CO2).

It has been observed that the preferred process is to provide a CO ₂ -containing gas by-product with a CO 2 content that is a certain proportion (eg, 10 to 50%) greater than the CO 2 content of the CO ₂ -containing stream. For example, the CO ₂ -containing stream may have a CO 2 content of approximately 15 wt.%, while the CO ₂ -containing gas by-product may have a CO 2 content of approximately 18 wt.% (which is 20% higher). This can be achieved without the additional expense of using a pure oxygen calciner, but rather by using control over the operating parameters of the calciner.

However, it should be noted that in alternative embodiments it is possible to carry out the process such that the recycled CO ₂ -containing gas by-product has a lower CO 2 concentration compared to the original CO ₂ -containing flue gas fed to the carbonization step, or typically the like. CO2 content. When the CO2 contents of the two gas streams are relatively variable, the relative proportions may be modified to produce a constant CO2 content supplied to the carbonation unit, or the two streams may be fed to carbonation without concentration control, resulting in a variable CO2 content in the reacting gas. It is also noted that the two CO ₂ -containing streams can be fed into the same carbonation vessel through different feed inlets, or the same feed inlet, or they can be fed into different carbonation vessels, or a combination thereof.

Examples and experiments

Study 1. Wet carbonization of chrysotile mining residues.

The first set of experiments is carried out using chrysotile mining residues consisting of lizardite, antigorite, brucite, iron oxides, chromium oxides and low chrysotile content to optimize wet carbonation conditions on a sample size of approximately 7 g with a granule size below 75 µm and a pulp density of 15 % (weight 150 g of solid per liter of liquid). The reaction temperature and duration are stable at 25°C and 6 hours, respectively. The variables are pressure, NaCl and NaHCO ₃ content, and whether the sample is heat-treated or not. They are optimized based on the percentage of CO2 removed and the percentage of solid carbonate formed (dependent variables). In table 1 shows different conditions and the results obtained.

From this table it can be seen that CO2 removal up to 87% can be achieved at a pressure of 10.2 atm. and for a heat-treated sample. Apparently, CO2 removal does not depend on the NaCl content and weakly depends on the NaHCO ₃ content in the solution, although thermal pretreatment is required. Within 6 hours under these conditions, 24% of the sample was carbonized.

- 14 043813

Table 1

Box-Behnken matrix for the first group of analyzes and results (T=25°C, t=6 h)

Experience Pressure NaCl _NaHCO3 Thermal CO2 removal Education (atm.) (M) (M) preliminary (%) solid treatment carbonate (%) 1 45.9 0.5 0.32 Yes thirty 0 2 10.2 0.5 0.64 Yes 78 5.43 3 10.2 1 0.32 No 49 2.24 4 10.2 0.5 0 Yes 79 19.13 5 45.9 1 0 No 21 0 6 45.9 0.5 0.32 No 27 0.4 7 81.7 1 0.32 No 23 0.16 8 81.7 0.5 0.64 No 10 0.91 9 10.2 0 0.32 No 44 0.72 10 45.9 0.5 0.32 No 15 0.4 AND 81.7 1 0.32 Yes 31 0.19 12 45.9 0.5 0.32 Yes 35 0.66 13 45.9 0 0 Yes 28 0 14 45.9 0.5 0.32 No 15 0.68 15 45.9 0.5 0.32 No 13 0.33 16 45.9 1 0.64 No 19 0.87 17 45.9 0.5 0.32 Yes 45 0 18 10.2 1 0.32 Yes 84 37.06 19 45.9 1 0.64 Yes 31 1.22 20 45.9 1 0 Yes 29 0 21 45.9 0 0.64 No 20 0.88 22 45.9 0.5 0.32 No 31 0.52 23 10.2 0.5 0 No 46 0 24 81.7 0 0.32 Yes 32 1.21 25 45.9 0.5 0.32 Yes 32 0.36 26 10.2 0.5 0.64 No 42 2.88 27 45.9 0 0.64 Yes 38 0.6 28 81.7 0 0.32 No 13 0.57 29 81.7 0.5 0 Yes 32 0 thirty 81.7 0.5 0.64 Yes 37 1.25 31 45.9 0.5 0.32 Yes 36 0 32 45.9 0 0 No 20 0 33 81.7 0.5 0 No 10 0 34 10.2 0 0.32 Yes 87 40.01

The duration of 6 h for carbonation under optimal conditions is very long, carbonation assays are carried out over shorter reaction times to test the time dependence of the wet carbonation rate. The experimental conditions and results are presented in table. 2. The temperature is kept constant at 25°C and the pulp density is kept constant at 15%.

- 15 043813

table 2

Experimental conditions and results of wet carbonization of a thermally _______________treated sample for 30 min______________

At the entrance

Time (min) Liquid volume (ml) Sample weight (G) Pressure (atm.) CO ₂ removal (%) RSO ₂ (atm.) A 30 50 7.02 AND 2 18.2 2.03 At 30 50 6.90 10.3 18.2 1.87 From 30 50 6.87 10.8 18.2 1.96 At the exit A loss Finite Finite Final Final RSO ₂ from ₂ volume of liquid sample weight pressure CO ₂ removal (%) (ml) (G) (atm.) (%) (atm.) A 83 45 6.81 9.05 3.9 0.35 B 82 45 6.84 8.64 4.0 0.35 C 82 43 6.80 8.57 4.1 0.35

Removal of 82% CO ₂ was achieved after a 30 minute reaction time.

Study 2. Wet carbonization of serpentinite.

This experiment describes the applicability of the method for treating a batch of gas containing 18.2% carbon dioxide for 15 minutes. The gas/liquid ratio (GLR) is fixed at 300%, which corresponds to a volume of carbon dioxide containing gas of 225 ml and a volume of water of 75 ml. The resulting aqueous slurry had a solids concentration of 15 wt%. The reaction temperature is set equal to the ambient temperature (18-25°C). A pressure of 10.5 bar is applied, which corresponds to an amount of 0.78 g CO ₂ at 20°C. After reaching pressure, all reactor valves are closed and the reaction proceeds for 15 minutes. The resulting carbon dioxide-depleted gas is then collected through a bag. The concentration of carbon dioxide in the carbon dioxide-depleted gas is measured using a CO ₂ analyzer. The resulting aqueous suspension is filtered and samples are taken for analysis.

The reaction at ambient temperature at 10.5 bar for 15 minutes showed a CO ₂ removal efficiency of 88±1%, as shown in the table. 3.

Table 3

Carbon dioxide mass balance during a 15-minute reaction at 10.5 bar (number of analyzes equal to 3)

Entrance Exit Processed with ₂ Efficiency CO ₂ (gCO ₂ ) 0.80 ±0.02 0.09 ±0.01 0.71 ±0.02 88 ±1%

Study 3: Optimization of thermal pretreatment of serpentinite prior to wet carbonization.

Another set of experiments was carried out to demonstrate that thermal pretreatment of the alkaline earth metal containing material resulted in good removal of carbon dioxide from the carbon dioxide containing gas.

The residue from serpentinite-based mining is used as an alkaline earth metal containing substance. First, depending on the size of the granules, the residue is crushed and then ground. The best results are obtained with samples with a particle size of less than 45 µm (median size 10 µm). To obtain a chemically reactive substance, the residue from serpentinite-based mining had to be further pre-treated to dehydroxylate the serpentinite. By removing water from different mineral crystal structures, the chemical structure of the sample changes and thus reduces the bound energy. It is well known that thermal activation of hydrated silicates promotes chemical activation prior to leaching [Nagamori et al. (1980) Activation of magnesia in serpentine by calcination and the chemical utilization of asbestos tailings - A review. CIM Bulletin 73, pp. 144-156].

Optimization of thermal pre-treatment is carried out taking into account the concentration of magnesium after leaching, dissolving in water (glass). Regarding FIG. 5 and 6, study the influence of temperature and pretreatment time, and pulp density during extraction for 30 min in water with stirring at 600 rpm. According to thermogravimetric analysis, the main mass loss of the studied sample is observed at 650°C. Thermal activation experiments showed that the best results were obtained after a 30-minute treatment at 650°C with a weight loss of approximately 10%.

- 16 043813

Study 4: Optimization of reaction parameters for wet carbonation.

Another series of experiments is carried out to optimize the reaction parameters, including carbonation pressure, reaction time, gas/liquid ratio (GLR) and water slurry density. To increase the solubility of carbon dioxide gas in water, the reaction temperature is set to room temperature (18-25°C), since the solubility increased at lower temperatures. Pressure is a key parameter of the process, as it affects the amount of carbon dioxide introduced into the reactor.

The experiments are carried out with a gas containing carbon dioxide, the characteristics of which are comparable to the flue gas of a cement plant. Accordingly, the composition is 18.2% CO2, 4.11% O2 and 77.69% N2. Reactions were performed in a 300 mL stirred tank reactor from Parr Instrument Company, Moline, IL, USA.

Pressure.

Tests on the effect of pressure showed that operating at low pressure did not affect the efficiency of the reaction. In reality, the decreasing pressure causes a small amount of carbon dioxide to be introduced into the reactor. For batch experiments, a pressure of 10.5 bar is set to maintain a certain amount of carbon dioxide introduced into the reactor.

FGZ and pulp density.

Parameters such as gas/liquid ratio (GLR) and pulp density are determined through a set of experiments with a reaction time of 30 min. Reducing the SGL did not affect the removal of carbon dioxide from the flue gas, but it did reduce the amount of carbon dioxide introduced into the reactor. On the other hand, the amount of flue gas processed was lower when the pulp density was set to 5%. To increase the amount of gas processed, experiments on SGL and pulp density are performed with a subsequent portion of gas.

Since the goal is to form alkaline earth metal carbonates for resale, it is important to have the final product as pure as possible. Experiments with 100% SGL and 15% slurry density showed that a significant amount of carbonates precipitated inside the reactor. However, it may be necessary to precipitate the carbonates outside the reactor in order to easily separate the precipitated carbonates and then obtain carbonates with a high purity of approximately 95%. In fig. Figure 7 shows that good CO2 removal yields and a high concentration of magnesium in solution occur with an aqueous suspension with a pulp density of 15% and a SGL of 300%.

Once the basic reaction parameters were adjusted, the reaction time was reduced.

Reaction time.

A series of experiments is carried out to reduce reaction time. In fig. Figure 8 shows the carbon dioxide removal results. Removal was 56% for a reaction time of 5 minutes and 83% for a reaction time of 10 minutes. The same effectiveness as observed for 30 min was achieved after 15 min. However, the amount of magnesium present in the solution is multiplied by 1.45, so 341 mg/L for 30 minutes compared to 495 mg/L for 15 minutes. A residence time of 15 minutes is acceptable for industrial applications and provides better magnesium solubility efficiency.

Study 5. Wet carbonization of serpentinite during continuous operation.

The experiment is carried out under continuous operation conditions. The goal was to confirm the feasibility of the reaction under mild pressure and temperature conditions. The flow of carbon dioxide-containing gas is controlled using a mass flow controller. The pressure in the reactor is controlled using a pressure gauge valve set at the required pressure. The experiment is carried out at 3.4 bar with a carbon dioxide gas flow of 42 ml/min (7.64 ml CO ₂ /min). Regarding FIG. 9, after an equilibrium phase of approximately 50 minutes, it was observed that the carbon dioxide removal efficiency remained constant at more than 98% for 130 minutes. Efficiency then decreased in a linear manner. As a result, the total amount of carbon dioxide reacted was 2.61 g CO2 out of 3.19 g of CO2 introduced. Compared to the initial magnesium content in the substance introduced into the reactor, the total leaching of magnesium was 50.8%.

Study 6: Reuse option.

The reuse option is based on treating multiple batches of carbon dioxide-containing gas with recycle solid streams and liquid streams. Experiments are carried out on a series of 6 batches of gas under the same conditions as defined in example 2. In this invention, the term batch is defined as 225 ml of gas (0.78 g CO2) at 10.5 bar, reacting for 15 minutes with stirring 600 rpm

The aqueous slurry, which consists of 15% solids in 75 ml of water, is brought into contact with two batches of carbon dioxide-containing gas before being filtered into a solid phase and an aqueous phase. The same filtered solid is again mixed with 75 ml of new water (or recycle water) to contact two more batches of carbon dioxide gas. The process is repeated with a total of 6 batches of gas containing carbon dioxide. After each filtration, the filtered aqueous stream, which is rich in dissolved magnesium and carbon dioxide, is fed into

- 17 043813 precipitator for the precipitation of magnesium carbonates.

Precipitation conditions are set at 40°C with stirring at 300 rpm. The filtered solids, after being contacted with 6 batches of gas containing carbon dioxide, are crushed and heated to promote additional leaching of magnesium. The treated solid is then reused in the reactor to contact 6 more batches of gas containing carbon dioxide.

Therefore, a total of 12 batches of gas containing carbon dioxide are treated with the same solid phase. The aqueous phase is filtered after contacting two batches of carbon dioxide-containing gas, and fresh water is used after contacting two batches of carbon dioxide-containing gas.

The results are summarized in table. 4. Carbonation of the solid is 64% after contacting 12 batches, assuming that all magnesium contained in the aqueous phase has precipitated.

Table 4

Amount of _CO2 processed ( _gCO2 ), CO2 removal efficiency and leaching __________________________Mg in 12 batches for 15 min. ______________________

The consignment 1 The consignment 2 The consignment 3 The consignment 4 The consignment 5 The consignment 6 The consignment 7 The consignment 8 The consignment 9 The consignment 10 Party I The consignment 12 Total Processed gas 0.68 0.69 0.67 0.61 0.56 0.41 0.44 0.59 0.53 0.42 0.27 0.29 6.14 gCO ₂ Efficiency 86% 87% 87% 77% 72% 51% 75% 65% 53% 34% 37% 21% 62% Leached Mg 14% 14% AND % 15% 7% 4% 64%

Study 7: Dry gas-solid carbonation.

Example 7 describes gas-solid dry carbonation experiments according to possible embodiments of the present invention.

In this series of experiments, the alkaline earth metal-containing substance was a residue from chrysotile mining from the Tetfor Min region directly at the exit of the residue conveyor. The chrysotile residue is crushed and ground to a mini-particle size of approximately 50 microns. The reaction occurred in a 4560 benchtop mini reactor from Parr Instrument Company. After the reaction, the gas is collected into 3.8 L Tedlar bags equipped with an on-off valve. Measure the concentration of carbon dioxide in the exhaust gas using a CO ₂ analyzer, Quantek Instruments, model 906.

Optimization of various parameters that can have a significant impact on direct dry gas-solid carbonation is carried out using both conventional single-variable-at-time methods and statistical response surface methodology.

Optimizing parameters using the conventional single variable method

A series of experiments are carried out to optimize the most suitable conditions for direct gas-solid dry carbonation with a conventional variation of one variable at a time. Carbonation efficiency at different temperatures and pressures is optimized based on the percentage of CO2 removal (dependent variable). Optimal conditions were assessed for raw, non-magnetic (Nemag) and heat-treated samples. Optimal conditions for each type of sample are given in Table. 5.

Table 5

Optimal conditions for direct dry gas-solid carbonation with different types of samples

Sample type Sample size (g) Heat treatment (°C, min) Temperature (°C) Pressure (atm.) Time (h) Average _CO2 removal (%) Raw 25 No 200 5 6 27.7±0.6 Non-magical 25 No 200 5 6 28.9±0.6 Raw 25 630, 30 200 5 6 36.8±2.4

The optimal operating conditions for direct dry carbonization were a pressure of 5 atm. and temperature 200°C for 6 h. Maximum CO2 removal of 36.8% was obtained with the raw heat-treated (at 630°C for 30 min and crushed) sample.

Optimization of parameters using the Box-Behnken plan.

The selected independent variables are temperature (X1), pressure (X2) and time (X3) and the selected independent response variables are CO ₂ removal, Y1 (%), and pressure change, Y2 (kPa). Since CO2 removal is a key factor in this experiment, the present study focused on the percentage of _CO2 removal. Therefore, percent CO ₂ removal was selected as the primary response surface in this model. A heat-treated (630°C for 30 min) sample weighing 25 g was used in all experiments.

In fig. 10 shows a response surface plot for CO2 removal (%) and from the said Figure it is clear that CO2 removal (%) is at its maximum value in the lower pressure and higher temperature range. The optimal conditions and confirmation of the optimized value are presented in Table. 6. Analysis of variance of the quadratic regression parameter for the predicted CO2 removal response surface (%) was analyzed using ANOVA.

The model F-value of 30.56 and the low probability value Beh > F less than 0.050 indicate that the model is significant. The multiple regression coefficients (R2=0.9752) show that only 2.5% of the total variation cannot be explained by the empirical model. This model can explain 97.5% of the response variability. The ^R2 value (0.9752) for CO2 removal (%) was found to be in reasonable agreement with the adjusted ^R2 value (0.9433). The predicted R ² (0.70) was in reasonable agreement with the adjusted R ² .

Optimal conditions for direct dry gas-solid carbonation using the Box-Behnken design were obtained at 258°C, 5.6 atm. for 310 min. A CO2 removal of 40.1% was predicted under the above conditions.

Model testing shows 37% CO2 removal, which is close to the predicted value.

Table 6

Response Surface Model (RSM) Validation Experiments

Experiments (No.) Temperature (°C) Pressure (atm.) Time (min) CO2 removal (%) MPO model 258* 5.53* 310* 40.1** A 258 5.53 310 37.9 IN 258 5.53 310 36.2 WITH 258 5.53 310 37.4

Average 37.1 ±0.8 *Optimal values of variables selected by the model.

**Predicted values for each response according to the model.

Carbonation studies are also carried out with a raw and non-magnetic sample under optimal conditions obtained from response surface methodology. Experiments and results are shown in table. 7 and this shows that under optimal conditions, the CO ₂ removal (%) for the three types of samples is in a similar range. This indicates that sample pretreatment does not have a significant effect on _CO2 removal (%).

Table 7

Experimental conditions and results of direct gas-solid dry carbonation for different types of samples under optimal conditions ______established using response surface methodology______

Sample type Temperature (°C) Pressure (atm.) Time (min) CO2 removal (%) Raw 258 3.95 310 35.7=1=1.1 Non-magical 258 2.96 310 35.7 Thermally 258 1.97 310 37.1=1=0.8

processed

Since the carbonation time under optimal conditions appears to be very long, 310 min, carbonation assays are performed at shorter reaction times to test the time dependence of the dry carbonation rate. Experiments and results are presented in table. 8.

Table 8 Experimental conditions and results of direct dry carbonization of a green sample at optimized temperature and pressure for 15 min

Experience Temperature (°C) Pressure (atm.) Time (min) CO2 removal (%) A 258 3.95 15 36.3 IN 258 2.96 15 39.0 WITH 258 1.97 15 33.5 Average 36.3±2.7

Based on the results, it was found that the main proportion of the reaction occurs at the initial stage of the carbonization reaction. The reaction achieved approximately 36% CO ₂ removal at 258°C, 5.53 atm. within 15 min. From this it can be assumed that the main share of carbonation occurs

- 19 043813 for a limited time, after which the reaction may become less important. The pressure change curve shown in Fig. 11 confirms the above statement. A sudden decrease in pressure in the initial minutes indicates that the reaction is occurring quickly at the beginning, and then a decrease in pressure becoming very slow or constant indicates that carbonation is occurring very slowly or has reached equilibrium. The increase in pressure and temperature immediately after adding the CO2 gas mixture may be due to the exothermic nature of the reaction. A decrease in reaction rate after a certain time may be due to the formation of a product layer, which may further impede the inward diffusion of CO2 and the outward diffusion of water. Also, a low surface renewal rate can reduce the rate of carbonation, which can be increased by increasing the rate of friction and particle abrasion through thorough mixing.

Study 8: Comparison of CO2 removal efficiencies.

Experiments are conducted to compare the CO2 removal efficiencies for wet and dry carbonation of various alkaline earth metal containing substances.

The results of wet carbonation are shown in table. 9, and the results of dry carbonation are shown in table. 10.

Table 9

Wet carbonation 150 g/l solid for 15 minutes at ambient temperature, P=10.5 bar

Test sample Thermal pre-treatment Average _CO2 inlet (g) Average CO ₂ output (g) Average % absorption from ₂ Standard deviation Bignel stone quarry (Saint-Urbain) anorthosite No 0.78 0.52 34.51 2.47 Bouchard stone quarry (Saint Urbain) - anorthosite No 0.78 0.43 44.37 10.18 old stone quarry Gen.electrique (Saint-Urbain)anorthosite No 0.76 0.45 40.51 15.49 andesine (BML stone quarry in Charlesbourg) No 0.78 0.47 39.77 7.66 concrete stone No 0.76 0.34 55.64 11.85 concrete with aggregates No 0.79 0.29 63.41 2.59 concrete No 0.78 0.17 78.44 1.21 steel slag No 0.76 0.12 84.51 4.23

- 20 043813

Red brick No 0.78 0.43 44.71 9.60 antigorite (stone quarry in Tetfor Min) Yes 0.78 0.32 58.89 2.94 sandstone (stone quarry in Montmagny) waste brick No 0.79 0.40 49.35 2.47 MgO No 0.77 0.43 44.62 2.23 (steelmaking) wollastonite (stone quarry No 0.78 0.46 40.80 2.04 Black Lake) olivine sand No 0.77 0.47 38.78 1.94 granite (stone quarry in Aguanish) No 0.77 0.49 37.06 1.85 magnesium-rich basalt (quarry in Saint-Joseph- No 0.80 0.54 32.90 1.64 de Beauce) calcium-rich basalt RayCar (quarry in No 0.77 0.55 28.68 1.43 Saint-Flavy) granite (stone quarry in Aguanish) Yes 0.77 0.57 25.12 1.26 CaO dust from rotary kiln No 0.77 0.04 95.38 4.77 MgO dust from rotary kiln No 0.75 0.05 93.20 4.66

- 21 043813

Table 10

Dry carbonation 1.5 g solid for 30 min at T=258°C, P=4 bar

Test sample Bignel stone quarry (Saint-Urbain) - anorthosite concrete concrete stone concrete with aggregates stone quarry Bouchard (Saint Urbain) - anorthosite old Gen.electrique (Saint Urbain) andesine (stone quarry BML in Charlesbourg) red brick steelmaking slag waste brick MgO (steel smelting) CaO dust from a rotary kiln sandstone (quarry in Montmagny) Thermal pre-treatment no no no no no no no no no no no no Average CO ₂ at inlet (g) 0.17 0.16 0.17 0.16 0.17 0.18 0.17 0.18 0.18 0.18 0.16 0.22 Average CO ₂ output (g) 0.09 0.02 0.04 0.07 0.09 0.03 0.10 0.10 0.09 0.05 0.10 0.14 Average _CO2 absorption (%) 43.37 74.83 74.79 58.03 46.98 81.14 39.90 41.07 47.18 70.67 37.99 34.08 Standard deviation 6.74 1.58 6.63 4.66 5.44 2.95 10.30 12.56 16.72 0.40 0.78 calcium-rich basalt RayCar (quarry in Sainte-Flavy) No 0.22 0.13 38.75 1.92

- 22 043813

magnesium-rich basalt (quarry in Saint-Josephde-Beauce) No 0.22 0.13 40.38 0.39 granite (stone quarry in Aguanish) No 0.22 0.13 40.10 0.78 granite (stone quarry in Aguanish) Yes 0.22 0.13 41.48 1.95 olivine sand No 0.22 0.12 43.13 1.17 wollastonite (Black Lake stone quarry) No 0.22 0.12 43.13 1.17 antigorite (stone quarry in Tetfor Min) Yes 0.22 0.13 42.31 0.78 Serpentinite (Black Lake) No 0.22 0.13 42.05 5.07 Serpentinite (Black Lake) Yes 0.22 0.14 23.2 5.82 MgO dust from rotary kiln No 0.22 0.14 37.34

Study 8. Preparation of magnesium oxide.

The following results illustrate the advantages of the method described in this invention for producing magnesium oxide compared to the conventional method. The following data was obtained from technical simulations performed using experimental data obtained from the serpentinite carbonization process. An assumption was made of zero CO2 loss during the overall MgCO ₃ roasting process. CO2 by-product emissions from roasting are calculated based on the total energy consumption of the process (carbonation + roasting = 1139 kWh/ton solids) and using stoichiometric equation 1. CO2 equivalent emissions (from other greenhouse gases) are not considered, but CO ₂ emissions are taken into account since they represent the main emissions in this scheme.

Heating

MdCO ₃ *ZN ₂ O -> MdO + CO ₂ + ZN ₂ O Equation 1

Based on Case 2, producing 179,000 tons of MgO per year would process 184,000 tons of CO2 from an industrial source and could result in 87,000 tons of CO2 emissions. For comparison, similar production of MgO according to the conventional method would produce 263,000 tons of CO2. Thus, the reduction in CO2 emissions is 176,000 tons of CO2, (263,000 - 87,000), giving a total saving of 360,000 tons of CO2 (176,000 + 184,000) per year.

Definition 9. Comparison of emissions.

CO2 emissions resulting from the MgCO ₃ roasting process may include 10 to 23% CO2. The processes described herein, which use Mg silicates to produce MgCO ₃ from flue gas (eg, 18.2% CO2), confirm the applicability of the CO2 emissions associated with the production of MgO as described. For example, the roasting emissions may include a similar CO ₂ content compared to the flue gas, and thus the carbonization step can use both the combustion gas and the roasting emissions as a source of CO ₂ with sufficient consistency for performance.

Study 10. Calcination of carbonates.

This refers to the calcination of nesquegonite (MgCO3.3H ₂ O), obtained by the methods described in this invention, to magnesium oxide (MgO) at 950°C. MgCO3.3H ₂ O is obtained in the precipitation step (step 32). Experiments are carried out in an electrically heated rotary kiln on a laboratory scale. The furnace had an internal diameter and length of 44.45 and 1000 mm, respectively. Firing was carried out by heating 5.0 g of the substance supplied at a constant speed of 0.18 g/min. The control panel set the oven speed to 3 rpm. The weight loss caused by heating was 68%. This highlights the decomposition of nesquegonite into MgO with loss of _CO2

Claims (38)

CLAIM 1. A method for producing magnesium oxide, including: producing magnesium carbonate by providing a magnesium-containing substance in an aqueous slurry and bringing CO ₂ -containing gas with said aqueous slurry to produce a carbonate-rich slurry; separation of magnesium carbonate from suspended matter saturated with carbonates; and subjecting the magnesium carbonate to calcination to produce a by-product of CO2 and magnesium oxide; wherein producing magnesium carbonate further comprises reusing at least one portion of the CO2 byproduct as a recycled CO2 byproduct and contacting said aqueous slurry with said recycled CO2 byproduct, wherein the recycled CO2 byproduct has a higher CO2 concentration than the specified CO ₂ -containing gas. 2. The method according to claim 1, additionally including: at the contacting stage, obtaining a carbonate-saturated slurry containing precipitated carbonates and substantially free of precipitated alkaline earth metal carbonates; separating the suspension saturated with carbonates into an aqueous phase containing precipitated carbonates and a solid phase; precipitation of magnesium carbonates from the aqueous phase; and separating magnesium carbonates from the aqueous phase. 3. The method according to claim 1 or 2, wherein the CO ₂ -containing gas includes CO ₂ -containing emissions, which are used immediately as they were received from the installation. 4. The method according to claim 3, where the CO ₂ -containing emissions are obtained at the stage of thermal activation of the magnesium-containing substance before being brought into contact with the CO ₂ -containing emissions. 5. The method of claim 3, wherein the CO ₂ -containing emissions include emissions from a separate emission source. 6. Method according to any one of claims 1 to 4, wherein the CO ₂ -containing gas used for contacting the magnesium-containing substance is obtained exclusively from a magnesium oxide production plant. 7. The method according to any one of claims 1-6, additionally including: subjecting the magnesium-containing substance to dehydroxylation to reduce the water content of the magnesium-containing substance and to obtain a thermally activated substance; and bringing the thermally activated substance into contact with the CO ₂ -containing gas. 8. The method of claim 7, wherein the dehydroxylation is performed at a temperature of about 600 to 700°C. 9. The method according to claim 8, where the dehydroxylation is carried out for approximately 20-60 minutes. 10. The method of any one of claims 1 to 9, wherein the magnesium-containing material is brought into contact with a CO ₂ feed stream that includes a plurality of CO ₂ feed streams. 11. The method of claim 10, further comprising controlling the relative amount of each CO ₂ feed stream in the CO ₂ feed stream. 12. The method according to claim 11, where the control is performed in accordance with the pressure, temperature and/or composition of the initial CO2 streams. 13. The method according to any one of claims 10 to 12, wherein the CO2 feed stream further comprises CO2 obtained from the additional magnesium oxide production line. 14. The method of claim 13, wherein the additional magnesium oxide production line includes a conventional production line. 15. The method according to any one of claims 1 to 14, wherein the magnesium-containing substance comprises serpentine or is derived from serpentinite or variants thereof. 16. The method according to any one of claims 1 to 15, where the magnesium-containing substance is obtained from at least one of: basalt, peridotite, serpentized peridotite, ophiolitic rock, mafic rock, ultramafic rocks, peridot, pyroxene, olivine, serpentine, minerals containing magnesium oxide, and/or brucite. 17. The method of claim 15 or 16, wherein the magnesium-containing substance is a magnesium-containing particulate material that has a magnesium content of between about 1 and about 35 weight percent. 18. The method of claim 17, wherein the magnesium content is from about 10 to about 30 wt.%. 19. The method according to any one of claims 1 to 18, where the magnesium-containing substance is obtained from mining residue. 20. The method according to claim 19, where the mining residue includes a residue from phyllosilicate mining and/or a residue from chrysotile mining. 21. The method according to any one of claims 1-20, additionally including: - 24 043813 subjecting a magnesium-containing substance to size reduction and removal of the magnetic fraction before carbonization. 22. The method according to claim 21, further including: grinding the starting material to a particle size of from about 200 to about 1000 microns to obtain a substance of the required size; removing the magnetic fraction from the crushed substance to obtain a non-magnetic fraction; and grinding the non-magnetic fraction to obtain a magnesium-containing substance having a particle size of no more than 75 microns. 23. The method according to any one of claims 1 to 22, where the firing is carried out in an indirectly heated firing installation. 24. Method according to any one of claims 1 to 22, wherein the firing is carried out in a directly heated firing unit. 25. The method of any one of claims 1 to 24, wherein the aqueous slurry is contacted with a CO2 feed stream comprising a _CO2 containing gas and a recycled CO2 byproduct, the method further comprising controlling at least one property of the CO2 feed stream. 26. The method of claim 25, wherein the control includes adjusting the relative amounts of CO2-containing gas and recycled _CO2 byproduct that are used to contact the magnesium-containing material. 27. The method according to claim 25 or 26, where the gas pressure, gas temperature and/or CO ₂ content in the CO ₂ feed stream brought into contact with the magnesium-containing substance are controlled. 28. The method according to any one of claims 1-27, additionally including: recovering the CO ₂ -containing by-product stream from the roasting process; and removing water from the _CO2 -containing byproduct to produce a treated CO2 byproduct stream before reusing at least one portion of the treated CO2 byproduct stream as a reused CO2 byproduct. 29. The method according to any one of claims 1 to 28, wherein the magnesium-containing substance includes evaporite. 30. The method according to claim 29, where the evaporite is obtained from an evaporation plant. 31. The method according to claim 29, where the evaporite contains a magnesium chloride salt. 32. The method according to claim 29, where the evaporite contains a magnesium sulfide salt. 33. The method according to claim 29, where the evaporite contains a magnesium carbonate salt. 34. The method according to any one of claims 1 to 33, wherein the CO2 content of the recycled CO2 by-product is at least 10% greater than that of the _CO2 -containing gas. 35. The method of claim 34, wherein the CO2 content of the recycled CO2 by-product is at least 20% greater than that of the _CO2 -containing gas. 36. The method of claim 34, wherein the CO2 content of the recycled CO2 by-product is at least 50% greater than that of the _CO2 -containing gas. 37. The method according to any one of claims 1 to 34, wherein the CO2 content of the reused CO2 by-product portion is from 15 to 25 wt.%, and the CO2 content of the CO ₂ -containing gas is from 10 to 20 wt.%. 38. A system for producing magnesium oxide, including: at least one carbonization plant having: a gas supply for receiving CO ₂ -containing gas, a suspension supply for receiving an aqueous suspension containing a magnesium-containing substance, a carbonation vessel for carbonating at least one portion of magnesium in an aqueous suspension with CO2 to produce a CO2-depleted gas and a carbonate-rich suspension containing precipitated magnesium carbonates , a slurry exhaust for removing carbonate-rich suspended matter containing precipitated magnesium carbonates, and a gas exhaust for removing CO2-depleted gas; separation plant having: a slurry supply for receiving a carbonate-rich slurry containing precipitable magnesium carbonates from a slurry outlet of the at least one carbonation unit, a separation chamber for separating the carbonate-rich slurry containing precipitable magnesium carbonates into a solid phase and an aqueous phase containing precipitable magnesium carbonates, and a liquid outlet for removing the aqueous phase, and a sedimentation unit having: supplying a suspension for receiving an aqueous phase containing precipitable magnesium carbonates from a liquid outlet of the separation unit, a settling chamber for precipitating magnesium carbonates and forming a sedimentary suspension, and a liquid outlet for removing the sedimentary suspension; a calcination unit for receiving at least one batch of magnesium carbonates, producing calcined magnesium oxide and a CO ₂ by-product stream; and a CO ₂ collection and supply system to collect the CO ₂ by-product stream and directly feed at a lower