EP4630374A1

EP4630374A1 - Apparatus for accelerated mineralization of carbon dioxide with by-products of industrial processes and related process

Info

Publication number: EP4630374A1
Application number: EP23847899.4A
Authority: EP
Inventors: Paolo BRAZZO; Ivana Moscato; David CALLEJO MUNOZ; Alessandro PANZA
Original assignee: Resilco Benefit Srl Soc
Current assignee: Resilco Benefit Srl Soc
Priority date: 2022-12-06
Filing date: 2023-12-06
Publication date: 2025-10-15
Also published as: WO2024121768A1; IT202200025125A1

Abstract

The present invention relates to an apparatus for the accelerated mineralization of carbon dioxide with by-products (slag) of industrial processes and a related process to achieve it. In particular, the apparatus of the invention allows to achieve a new industrial process for obtaining the mineralization of carbon dioxide in the solid carbonate forms of a precursor material comprising at least one of alkali, alkaline earth and transition metals and, possibly, carbonated synthetic carbonate materials, using a methodology which effectively accelerates the mineralization reaction thereof, avoiding the phenomenon of passivation inside the reactor. The aforesaid process relates to the activation of said by-products (slag) of industrial processing (henceforth referred to as 'precursors' for convenience) and the mineralization of carbon dioxide by means of the reaction with the aforementioned precursors.

Description

APPARATUS FOR ACCELERATED MINERALIZATION OF CARBON DIOXIDE WITH BY-PRODUCTS OF INDUSTRIAL PROCESSES AND RELATED PROCESS

TECHNICAL FIELD

The present invention relates to an apparatus for the accelerated mineralization of carbon dioxide with by-products (slag) of industrial processes and a related process to achieve it.

In particular, the apparatus of the invention allows to create a new industrial process for obtaining the mineralization of carbon dioxide, hereinafter also CO2, in the forms of solid carbonates of a precursor material comprising at least one of alkali, alkaline earth and transition metals and, possibly, carbonated synthetic carbonate materials, using a methodology which effectively accelerates the mineralization reaction thereof, avoiding the phenomenon of passivation inside the reactor.

The aforesaid process relates to the activation of said by-products (slag) of industrial processing (henceforth referred to as 'precursors' for convenience) and the mineralization of carbon dioxide by means of the reaction with the aforementioned precursors.

The materials obtainable from the process which is the subject matter of the invention are essentially mineral powders of carbonates of alkaline elements, alkaline earth and/or transition metals and, possibly, carbonated synthetic carbonate materials, derived from the substantially superficial carbonation of said industrial processing slag (precursors), and the aforesaid treated precursors having pozzolanic characteristics.

What are known as the treated precursors can be not carbonated, because they have not reacted with the CO2, or they can be only partially carbonated due to the residual CO2 still present in the wastewater, for recovery, which could react further with the precursor.

STATE OF THE ART

Carbonation technologies allow the achievement of two important objectives: the reduction of CO2, SO2 and NO2 greenhouse gases, and the practical utilization of the large amounts of special industrial waste with alkaline chemistry present throughout the world (steel mill slag, water treatment sludge, alumina red sludge, incineration slag, alkaline fly ash, and so on).

Carbonation is the crystallization process of carbonates by means of injected CO2. The technology behind carbonation has been studied more and more intensively because of the need to meet the demands to remove as much CO2 from the planet's atmosphere as possible, through what is known as Carbon Capture Storage (CCS). Among the CCS techniques, CO2 mineralization is undoubtedly the most adequate and least invasive. This is essentially for two reasons: because it produces materials which can be used immediately, the proceeds of which make these technologies more cost-effective, and because the CO2 stored remains permanently fixed.

From a quantitative point of view, we can make a prediction of the effects of carbonation on emissions. For example, take the case of a gas-fired power plant of the most modem type (e.g., Armaroli and Po, 2003). A 780 MW gas-fired power plant produces 2 Mt of CO2, 2700 t of NO2, 1500 t SO2, 1350 t of CO, 3200 t of hydrocarbons and benzene and 620 t of particulate matter annually. To break down such contents, at least 4 million tonnes of reagent are needed, which could consist of steel slag (in Italy about 6 Mt of slag from steel and cast iron production and 2 Mt of red alumina sludge per year).

Of these materials, about 3 million tonnes become carbonates, to be used as raw material in the preparation of lime and dolomite for the steel and cement industry, and 1 million tonnes of aluminium silicates and iron oxides. The latter part of spent reagents can easily be reintroduced into pozzolanic cement production cycles, with great advantages for the environment.

The carbonation is usually carried out using a source of CO2 (rarely air, more often compressed CO2), blown into aqueous solutions where alkaline ions or solids exchanging alkaline ions are present. There are diverse methods for obtaining carbonation and we can arbitrarily divide them into two categories:

Carbonation in solution, known as 'ex situ'

Carbonation in solution, known as 'in situ'

The first group of processes ('ex situ') is among those most frequently used. They involve the use of aqueous solutions where CO2 is injected pressurized and where the substances to be carbonated are present, either in solid or dissolved form. The ex situ technologies involve carbonation on minerals taken from their deposit, brought to a special plant, enriched and activated there (mechanically or thermally) and subjected to a carbonation reaction in reactors under pressure at controlled temperatures. For example, in the work of O'Connor et al. (2000) presented at the 2000 International Conference on Coal Utilization in Albany (OR, USA), described a technology that adopts serpentinite and olivine residues as precursors for carbon dioxide absorption. The idea was to use such materials to absorb the 10,000 tonnes of CO2 emitted per day by a 500 MW coal-fired power plant. The process which requires crushing and granulating the ore with relative size sorting (only granules smaller than 5 mm in average diameter) has a yield of about 83%.

From the above, it is clear that handling and processing thousands of tonnes of ore per day is only possible in sites where there is already a large amount of disused material, e.g., a mining dump. In such a condition, the CO2 cannot be pumped and maintained under supercritical conditions, which is a condition which can only be achieved in a closed, pressurized vessel, or at the moment of contact between the solution and the gas in input. This is why mention is made of the second group of processes ('z« situ'). The idea is, therefore, to create a dense network of air ducts within the mining dump, introduce a solution of water and sodium chloride and pump high-pressure CO2 into the ducts, so as to promote the mobility of the solution in the interstices between the ore granules. From this point of view, the technique is simple and economical: there is no preliminary grinding or conditioning, nor any handling of the ore. This involves bringing CCh from large users (e.g., steel mills, thermal power plants and cement kilns), at the outlet pressure of the flue gases (spent gases), directly to the landfill through a suitable pipeline, then pumping such fluid in a controlled manner into the basin and then activating the carbonation. The problem in this case is the reaction time, which can be considerably long.

In US 2010/141013 Al, a process and apparatus for sequestering CO2 in a waste gas within freshly crushed oligocene serpentine rock particles is described, using a specific apparatus to crush the rock up to obtaining small fragments in a pressurized gas atmosphere. The process selects the small fragments of crushed rock and, after absorbing the CO2, covers them with a cement coating for use as building material components. The apparatus comprises some parts which are only formally similar to those in the present patent application, however, its operation is completely different, its running costs are considerably high and it does not suggest how to effectively answer the technical problem described below.

EP 4 005 995 Al describes a process for transforming fly ash derived from combustion into starting materials for obtaining industrial products. The process comprises, inter alia, the injection of CO2 under pressure from 3 to 15 bar, thus differing substantially from the present patent application.

In DE 10 2008 039171 Al, a process and apparatus for separating CO2 from flue and exhaust gases is described. The process uses different types of reactions to capture the CO2 and thus, even if some of the reactor's constituent parts seem similar to those in the present patent application, their purpose and operation is overall completely different, thus not describing the characteristics thereof.

For all these reasons, there is a particular need to have an optimal reactor for the carbonation process and a related process which can provide high mineralization yields, recycling of produced wastewater and ease of use, as well as significant savings in the overall operating costs.

The main problems inherent in mineralization processes comprise, for example: the problem of precursor passivation; the insufficiently high rate of mineralization; the management of the concretionary masses formed in the reactors.

The first problem arises from the fact that the precursor granules, placed inside a liquid batch, tend to react from the surface of the granule inwards. Once a certain depth is reached, the exchange of the ions forming the carbonate compounds ceases with the outside, whereby the mineralization process stops. To attempt to overcome these drawbacks, attempts are made to reduce the size of the granules as much as possible through preliminary grinding processes, but this significantly increases the cost of the process.

The second problem depends on the solubility of CO2 at ambient pressure in water. The phenomenon of CO2 mineralization essentially occurs upon the contact between the CO2 molecules and the surface of the precursor mineral; thereby, water plays a fundamental role, both in removing the reactive cations from the mineral and in allowing the carbonate formation reaction to occur. On the other hand, a low solubility of cations (e.g., Ca²⁺ and Mg²⁺) and a low solubility of CO2 in water do not allow a high reaction rate. To give an example, consider a solubility of calcium hydroxide of 1.7 g/1 (20 mM/1) and CO2 equal to 1.48 g/1 (38 mM/1). Thus, forming one mole of CaCOs (PM = 100.09 g/M) requires 44 1 of mineralized water with Ca(OH)2 and 26 1 of water with dissolved CO2, respectively. In essence, one cubic metre of water would produce 14.3 kg of CaCCh, forming the dissolutions of 74 kg of calcium hydroxide and 44 kg of carbon dioxide. The yield in terms of water and time is thus extremely low.

The third problem concerns the inevitable formation of static concretionary masses inside the reactors, which create, in the long run, enormous problems for plant management, blocking valves and pipes.

OBJECTS AND SUMMARY OF THE INVENTION

It is the object of the present invention to overcome the drawbacks of the prior art. In particular, an object of the present invention is to make a new apparatus for the mineralization of carbon dioxide preferably in the forms of solid carbonates of alkali metals, alkaline earth and transition metals, and possibly of carbonated synthetic carbonate materials.

A further object of the present invention is to provide a process for the mineralization of carbon dioxide in the forms of solid carbonates of alkali metals, alkaline earth and transition metals, and possibly of carbonated synthetic carbonate materials.

A further object of the present invention is to have a process for the mineralization of carbon dioxide in the forms of solid carbonates of alkali metals, alkaline earth and transition metals, and possibly of carbonated synthetic carbonate materials, with the recycling of the reaction water.

A further object of the present invention is to have a process by which carbonates can also be obtained from the treatment of hazardous waste, such as 'fly ash' from municipal waste incineration, from which useful industrial products such as pozzolan can also be extracted.

A further object of the present invention is to have a process which allows to obtain processed precursors which can be used as raw materials in production cycles such as, but not limited to, the production of cements, concretes, building materials or road substrates.

These and other objects of the present invention are achieved by a system incorporating the features of the annexed claims, which form an integral part of the present description.

To fulfil the objects of the present invention, the precursor material for the process of the invention must preferably have the following characteristics: be a composition enriched in alkali with high reactivity in water at basic pH; have a controlled particle size, possibly less than 1 mm; be available in large amounts.

Furthermore, the precursor can, by way of example, be waste/slag such as steel mill slag, basic industrial sludge from civil and industrial wastewater, from paper mills, from alumina, zinc and titanium dioxide treatment processes (red sludge), and fly ash from incineration. Preferably, the precursor can additionally comprise an additive to make the reaction process with CO2 more efficient. By way of example, in the case of fly ash, the precursor is preferably additivated with sodium hydroxide (NaOH) to efficiently capture the CO2 in the reaction with calcium sulphate.

Such materials have very large volumetries, particle sizes often below 10 microns, and an extremely high alkali content. Of course, these materials also include mining waste, e.g., serpentine waste, iron and manganese mine waste, phosphoritic waste deposits, and the like.

In a first preferred embodiment, it is an object of the present invention an apparatus for the mineralization of carbon dioxide in the solid carbonate forms of a precursor material comprising at least one of alkali metals, alkaline earth metals, transition metals and carbonated synthetic carbonate materials, said apparatus comprising at least: a loading device (1) of a mixture of the precursor material suspended in water; a reactor (2) equipped with a plurality of inlet and/or outlet openings for the introduction of the mixture of the precursor material suspended in water and/or processing wastewater and for the emission of an aqueous suspension of the precursor; said reactor being further provided with stirring means and any suitable cooling means to counteract possible undesirable temperature increases (not depicted in the figure); a cavitation device (5) (static or dynamic) placed externally to said reactor and in fluid connection therewith, said cavitation device (5) being positioned along a recirculation circuit originating and flowing into the reactor (2); at least one device (7, 10,18), at the exit from said reactor (2), for the separation of the reaction products and the recovery of the relative wastewater; in which in particular there is at least one injection point (4a, 4b, 4c) of a gaseous mixture containing, or consisting of, CO2 placed upstream of the cavitation device (5). This apparatus is described in detail in the following description and in the attached Figure

1.

The process for mineralization of carbon dioxide using the apparatus of this first preferred embodiment of the invention essentially comprises the following steps: a) loading a suspension in water of said precursor material into a reactor (2) by means of a loading device (1), through a first opening of the reactor (la), e.g., through a hopper or similar functionalities selected preferably from those known in the art; b) intercepting, through a second opening of the reactor (lb), said aqueous suspension of the precursor by means of a pump (3) and pumping it through a cavitation device (5), together with a gaseous stream containing, or consisting of, CO2 fed to the aqueous suspension of the precursor upstream of the cavitation device (5); c) reintroducing into the reactor, through a third opening (1c) thereof, the flow in output from said cavitation device (5) and continuing the cycle of the cavitation process until a constant desired pH is obtained in the reactor.

The process for the mineralization of carbon dioxide can further comprise at least one of the following steps: d) sending, through a fourth opening (Id) of the reactor, by means of a pump (6), a suspension resulting from step c) into a first separation device (7) and separating the components of said suspension to give, respectively, a final solid (substantially consisting of carbonates and carbonated precursor) and wastewater, or a partially carbonated solid and a liquid enriched in alkali; and/or e) discharging a residual content on a bottom of the reactor (2), through a further opening (1g) located on the bottom thereof, into a further separation device (10) and separating the components thereof to give a sludge flow (11) (mainly consisting of treated and essentially unreacted precursor) and a wastewater flow (12) to be sent for disposal or recycled, re-introducing it in the reactor.

In a second preferred embodiment (substantially analogous to the first, but only partially modified by the addition of certain embodiment variants), an object of the present invention is an apparatus for the mineralization of carbon dioxide in the solid carbonate forms of alkali metals, alkaline earth and transition metals as described above, at least comprising: a device for loading a mixture of precursor material (industrial slag) and water; a reaction and mixing chamber/tank (the 'reactor') equipped with a plurality of inlet or outlet openings (i.e., loading or unloading) and stirring means, as described above; a cavitation device placed externally to the reactor and in fluid connection therewith, the cavitation device being placed along a recirculation circuit originating and flowing into the reactor; at least one device for separating reaction products and recovering wastewater located at the exit from the reactor; in which, in particular, at least one injection point of a gaseous mixture containing, or consisting of, CO2 is provided upstream of the cavitation device and in which the cavitation device comprises at least one passive cavitator and at least one active cavitator downstream of the passive cavitator.

In a third preferred embodiment (substantially analogous to the first, but only partially modified by the addition of certain embodiment variants), an object of the present invention is an apparatus for the mineralization of carbon dioxide in the solid carbonate forms of alkali metals, alkaline earth and transition metals as described above, at least comprising: a device for loading a mixture of precursor material (industrial slag) and water; a reaction and mixing chamber/tank (the 'reactor') provided with a number of appropriate inlet or outlet (i.e., loading or unloading) openings for performing the various, necessary, functional operations associated with the execution of the process of the invention as described above; said reactor being further provided with stirring means and any appropriate cooling means to counteract possible undesirable temperature increases (not depicted in the figure); a cavitation device (static or dynamic) placed externally to said reactor and in fluid connection therewith; devices (preferably, three) for the separation of solid or sludge products of the process and for the recovery of wastewater; an additional collection/accumulation tank for the liquid reacted in the reactor and stripped/separated from the solids; an additional abatement tower (e.g., a 'scrubber') for gas abatement.

This apparatus is described in detail in the following description and in the attached Figure 3.

The process for mineralization of carbon dioxide using the apparatus of this third preferred embodiment of the invention essentially comprises the following steps: a) loading, e.g., through a hopper or similar functionalities, as described above, a mixture (suspension) of precursor material and water into reactor B (see 2.) of Figure 2); b) passing the suspension of said precursor-water mixture, together with a gaseous stream containing, or consisting of, CO2, through the cavitation device mentioned above, then reintroducing into the reactor the fluid phase resulting from the cavitation and continuing the process until the desired constant pH is achieved; c) directing the suspension obtained from step b) towards a first separator to provide a partially reacted solid (a precursor), which is re-introduced into the reactor, and a clear liquid enriched in alkali, which is directed to a suitable collection tank outside the reactor (this occurs because the precursor in water releases alkalinity and cavitation greatly intensifies this effect; in other words, the 'partially reacted' solid obtained is a solid which has released a part of its alkalinity but can still release more thereof, whereby it is re-introduced into the reactor); d) direct said liquid enriched in alkali into a gas abatement tower (e.g., a scrubber), where it is atomized and hit by a gaseous stream containing, or consisting of, CO2 to give a suspension of water and carbonates; e) direct the suspension of water and carbonates obtained in d) into a second separator to give a solid substantially consisting of a mixture of carbonates.

Similarly to what has already been described above, the aforesaid process can further comprise the following steps: f) discharging from the bottom of the reactor into an external third separator and separating from the water a sludge stream consisting mainly of treated and essentially unreacted precursor; g) sending the wastewater, separated from said sludge in step f) above, for disposal or recycling it by re-introducing it into the reactor.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, objects and advantages of the present invention will become clearer from the detailed description which follows made with reference to the attached figures. It is in any case to be noted that there is no intention to limit the invention to the specific embodiment illustrated in said figures, rather on the contrary, the invention intends covering all the modifications, alternative and equivalent constructions and variants which fall within the scope of the invention as defined in the attached claims.

Figure 1 schematically depicts a first preferred embodiment of an apparatus for the accelerated mineralization of carbon dioxide according to the present invention.

Figure 2 schematically depicts a second preferred embodiment, partially varied from the previous one, of an apparatus for the accelerated mineralization of carbon dioxide according to the present invention.

Figure 3 schematically depicts a third preferred embodiment, partially varied from the embodiment of Figure 1, of an apparatus for the accelerated mineralization of carbon dioxide according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

Unless otherwise defined, all the terms of the art, notations and other scientific terms used herein are intended to have the meanings commonly understood by those skilled in the art to which this description belongs. In some cases, terms with commonly understood meanings are defined herein for clarity’s sake and/or ready reference; the insertion of such definitions in the present description must therefore not be interpreted as representative of a substantial difference with respect to what is generally understood in the art.

The terms “comprising”, “having”, “including” and “containing” are to be understood as open terms (i.e. the meaning “comprising, but not limited to”) and are to be considered as a support also for terms such as “essentially consist of’, “essentially consisting of’, “to consist of’ or “consisting of’.

The use of “for example”, “etc.”, “or” indicates non-exclusive alternatives without limitation, unless otherwise indicated. The use of “comprises” and “includes” means “comprises or includes, but not limited to”, unless otherwise indicated.

With regard to the detailed description of the invention with particular reference to the appended figures, they schematically depict the preferred equipment and process scheme(s) of the present invention, albeit in a non-limiting manner for the person skilled in the art, respectively, as described below.

In particular, Figure 1 illustrates: 1) a loading device for loading the precursor-water mixture in the mixing reactor, such as a hopper; la) a first inlet opening in the reactor (i.e., the opening for loading the materials to be processed); lb) a second outlet opening in the reactor (for sending the precursor-water suspension, loaded through la), to a cavitation device or cavitator; 1c) a third inlet opening in the reactor (for the re-introduction therein of the fluid flow subjected to cavitation coming from the cavitator) Id) a fourth outlet opening of the reactor (for sending the suspension subjected to cavitation to a first separator 7)); le) a fifth inlet opening to the reactor (for the re-introduction therein of the flow of wastewater coming from the first separator, mentioned above); If) a sixth outlet opening of the reactor (for the discharge from the bottom thereof of the treated reaction sludge which has not reacted, or which is only partially carbonated); 2.) the reactor (formed by a mixing and reaction chamber provided with the loading and unloading openings described above and with stirring means and possible cooling means, not described in the figure); 3.) a pump which, from the reactor, directs the suspension of the precursor- water mixture towards the cavitator, together with a gaseous mixture containing, or consisting of, CO2; 4.), 4a), 4b), and 4c) injection points of the gaseous mixture containing, or consisting of, CO2; 5.) a cavitation device containing one or more cavitating elements, static or dynamic, selected from suitable ones commonly commercially available, placed along a recirculation circuit originating from and flowing into the reactor; 6.); a pump which, from the reactor, directs the suspension subjected to cavitation towards a first separator; 7.) a first separator, which separates the solid portion of the suspension described above from its aqueous portion; 8.) final solid, separated in 7.) from the water (substantially consisting of a mixture of a portion of carbonated precursor + carbonates); 9.), wastewater flow, separated in 7.) from the solid 8.), which is reintegrated into the cycle (i.e., re-introduced into the reactor through the opening le)); 10.) a second separator, connected with the outlet from the bottom of the reactor If); 11.) flow of reaction sludge mainly consisting of the portion of the precursor treated and substantially unreacted; 12.) flow of wastewater, separated from said sludge, which is sent for disposal or recycling by re-introducing it into the reactor, analogous to the flow 9.

Accordingly, as schematically illustrated in the attached Figure 1, in the first preferred embodiment of the process of the invention, a flow 1.), consisting of water and precursor, is introduced into the mixing reactor 2.) through a first opening la). Such a reactor can have a flat bottom, a conical bottom or a slanted bottom. The addition of material into the reactor can be performed, for example, through a hopper, or similar devices, using systems such as a rotovalve, or an auger. The concentration of slag in water is on average comprised from 0.5% to 50% w:w (i.e., weightweight), more preferably from 1% to 20% w:w. In the reactor, the suspension of precursor in water is intercepted through a second opening lb) by a pump 3.) and pumped through the cavitation device 5.). Such a device can be formed by one or more cavitation elements, static or dynamic, known in the art and selected from those suitable for the purpose. Such a device can further comprise at least one passive cavitator, or at least one active cavitator, or a plurality of cavitators comprising at least one passive cavitator and at least one active cavitator.

Before the cavitation device, a gaseous stream containing, or consisting of, CO2 4.) is injected in different injection points upstream of the cavitation device 5.), such as 4a) in the reactor, or 4b) outside the reactor, before the pump 3.), or 4c) after the pump 3, but before the cavitation device 5.). The injected gas can consist of an artificial mixture of air and carbon dioxide (in which the concentration of carbon dioxide can vary from 1% to 100%), or (exhaust) fumes, containing carbon dioxide in a concentration of at least 1%, deriving, for example, from industrial processes. The resulting mixture exiting the cavitation device 5.) is re-introduced into the reactor 2.) through a third opening 1c).

If the cavitation device 5.) comprises both at least one passive cavitator and at least one active cavitator, the at least one passive cavitator is preferably placed upstream of the at least one active cavitator. Advantageously, the homogenising action of the passive cavitator on the gaseous mixture containing, or consisting of, CO2 comprised in the aqueous suspension of the precursor results in a micronization of the bubbles in the gaseous mixture, significantly improving the performance of the active cavitator working on an essentially continuous fluid.

The cavitation process is continued until a pH between 10 and 6, more preferably between 9 and 7, is obtained in the reactor, after which the residual solid part is separated from the liquid part. Through a fourth opening Id), a pump 6.) passes the suspension which has interacted with the cavitation device 5.) through a first separator 7.). Such a first separator can be, for example, but not limited to, selected from a hydro-cyclone separator and/or a settler and/or a flotation chamber and/or a bag and/or a tank and/or a drainage belt and/or a centrifuge and/or a filter press. From such a first separator 7.) a flow 8.) containing the final solid product (substantially consisting of a mixture of carbonated precursor and carbonates, which can be separated later, separately), and a flow 9.) of wastewater is obtained in output, which is re-introduced back into the reactor 2.) through a fifth opening le).

The reactor 2.) also has a sixth opening If) from which the residual contents of the reactor can be discharged, more preferably, the portion of the suspension which settles at the bottom of the reactor, conveying it into a second separator 10.) (similar or equal to the first above). In output from this second separator 10.), a sludge 11.) is obtained, containing the unreacted, or only partially carbonated, treated precursor, which can be used in the same use context as the carbonated material, and a wastewater flow 12.) which can be sent for disposal, or re-introduced in circulation in the reactor 2.) similarly to the flow 9.).

In turn, Figure 2 illustrates a second embodiment of an apparatus for the accelerated mineralization of carbon dioxide according to the present invention which differs from the first embodiment in that along the recirculation circuit, upstream of the cavitation device 5.), an oxygenator element is placed, preferably an element in the serpentine form 24.).

In this case, there is at least one injection point 4.) of a gaseous mixture containing CO2 located upstream of the serpentine element 24.), such as in the reactor (4a) or (4b) outside the reactor, but before the pump 3.), or 4c) after the pump 3.), but before the serpentine element 24.). Advantageously, in this configuration, the serpentine element 24.) increases the path travelled by the aqueous suspension of the precursor mixed with the gaseous mixture containing, or consisting of, CO2, increasing the reaction time between the precursor and the mixture.

In turn, Figure 3 illustrates: 1.) a loading device for loading the precursor-water mixture into the reactor; la) a first inlet opening into the reactor (i.e., the opening for loading the materials to be processed); lb) a second outlet opening from the reactor (for sending the precursor-water suspension loaded through la to the cavitator); 1c) a third inlet opening into the reactor (for the re-introduction therein of the fluid flow subjected to cavitation coming from the cavitator) Id) a fourth outlet opening from the reactor (for sending the suspension subjected to cavitation to a first separator); le) a fifth inlet opening in the reactor (for the re-introduction therein of the solid, which has yielded alkalinity, or which has been partially carbonated, separated in the first separator described above); If) a sixth opening, through which the wastewater in output from the second separator 18.) is reintroduced into the reactor; 1g) a seventh outlet opening from the reactor (for the discharge from the bottom thereof of the treated and unreacted, or only partially carbonated, reaction sludge); 2.) the reactor (consisting of a mixing and reaction chamber equipped with the loading and unloading openings described above and with stirring and possible cooling means, not described in the figure); 3.) a pump which, from the reactor, directs the suspension of the precursorwater mixture towards the cavitator, together with a gaseous mixture containing, or consisting of, CO2; 4.), 4a), 4b), and 4c) points for injecting a gaseous mixture containing, or consisting of, CO2; 5.) a cavitation device containing one or more cavitating elements equal to those shown for Figure 1 and placed along a recirculation circuit originating from and flowing into the reactor; 6.) a pump which, from the reactor, directs the suspension subjected to cavitation towards a first separator; 7.) the first separator, which separates the solid portion of the suspension subjected to cavitation described above from its aqueous portion; 8.) the solid separated in 7.), which is re-introduced in the reactor 2.); 9.) liquid enriched in alkali, separated in 7.) from the solid 8.), which is directed to an accumulation tank; 21.) the accumulation tank, external to the reactor, containing the aforesaid liquid enriched in alkali, which is sent to a scrubber; 22.) a pump which directs the aforesaid liquid enriched in alkali from the tank 21.) to the scrubber; 23.) where the treatment of the aforesaid liquid enriched in alkali with a gaseous stream containing CO2 occurs; 23a) liquid enriched in alkali from the tank 21.), atomized; 13.) gaseous current containing, or consisting of, CO2, which washes the aforesaid atomized liquid enriched in alkali in a counter-current; 14.) the aforesaid gaseous current containing CO2 in output from the scrubber after having performed the washing treatment of the alkali-enriched, atomized liquid; 15.) suspension of water and solid carbonates obtained from the aforesaid washing with CO2 of the liquid enriched in alkali; 16.) a pump which directs the aforesaid suspension of water and solid carbonates from the scrubber 12.) towards a second separator; 17.) injection of a flocculating agent before entering the second separator; 18.) the second separator which separates the solid carbonates of the flocculated suspension from their aqueous portion; 19.) solid carbonates separated in 18.); 20.) water separated in 18.) from the solid 19.), which is recycled, re-introducing it into the reactor 2.); 10.) a third separator connected with the outlet from the bottom of the reactor 1g); 11.) flow of reaction sludge (consisting of the treated and substantially unreacted portion of the precursor; 12.) wastewater flow, separated from said sludge, which is sent for disposal, or for recycling by re-introducing it into the reactor, analogous to the flow 20.

Accordingly, as schematically illustrated in the attached Figure 3, in the second preferred embodiment of the process of the invention, a flow 1.), consisting of water and precursor, is introduced into the mixing reactor 2.) through a first opening la). The concentration of slag in water can be comprised from 0.5% to 50% w:w (i.e., weightweight), more preferably from 1% to 20% w:w. In the reactor, the suspension of precursor in water is intercepted through a second opening (lb) by a pump 3.) and pumped through the cavitation device 5.). Such a device can consist of one or more cavitation elements, either static or dynamic, or a combination thereof, suitably selected from those known and commercially available. Such a device can further comprise at least one passive cavitator, or at least one active cavitator, or a plurality of cavitators comprising at least one passive cavitator and at least one active cavitator, such as described above. A gaseous mixture containing, or consisting of, CO2 4.) is injected upstream of the cavitation device in various injection points placed upstream of the cavitation device 5.), such as in the reactor (4a) or (4b) outside the reactor, but before the pump 3.), or 4c) after the pump 3.), but before the cavitation device 5.). The injected gas can consist of an artificial mixture of air and carbon dioxide (in which the concentration of carbon dioxide can vary from 1% to 100%), or (exhaust) fumes, containing carbon dioxide in a concentration of at least 1% for example, deriving from industrial processes. The mixture exiting the cavitation device 5.) is re-introduced into the reactor 2.) through a third opening (1c).

Through a fourth opening (Id), a pump 6.) transports the suspension which has interacted with the cavitation device 5.) through a first separator 7.). Such a first separator can be, for example, a hydrocyclonic separator, or another appropriate separation device such as those described above. From such a first separator, a flow 8.) consisting of the separated solid is obtained at the outlet, which is made to re-enter the reactor 2.) through a fifth opening (le), while the flow 9.) consisting of the alkali-enriched water separated in 7.) is sent to a collection tank 21.

From such a tank, the liquid enriched in alkali is withdrawn by means of a pump 22.) and sent to an abatement tower 23.), where it is atomized by means of special nozzles (23a). Such a tower can be, for example, a scrubber for gas abatement. A gaseous stream containing CO2 13.) is introduced into the scrubber 23.), which passes through the chamber and comes into contact with the atomized liquid (12a).

Subsequently, the residual gaseous stream 14.) exits the reactor. The gas 13.) can be an artificial mixture of air and carbon dioxide (in which the concentration of carbon dioxide can vary from 1% to 100%), or (exhaust) fumes, containing carbon dioxide in a concentration of at least 1% for example, deriving from industrial processes. The gas in output 14.) contains a lower concentration of carbon dioxide than the flow in input 13.).

On the bottom of the scrubber there is a suspension 15.) in which the solids formed by the interaction of the fluid (23a) with the gas stream 13.) accumulate. Such a suspension is withdrawn, for example, by means of a pump 16.) and sent to a second separator 18.), before which a flow 17.) can be added, which contains a flocculation or coagulation promoter.

In output from the second separator 18.), a flow 19.) consisting of the solid end product (a mixture of carbonates) and a wastewater flow 20.) is obtained, which is re-introduced in the reactor 2.) through a sixth opening (If). The reactor also has a final opening (1g) from which the residual contents of the reactor can be discharged, more preferably, the part settling on the bottom, and conveyed into a third external separator 10.).

In output from the third separator, a sludge flow 11.) is obtained containing the treated and unreacted precursor, or only partially carbonated precursor, which can be used for other applications, and a wastewater flow 12.) which can be disposed of or re-introduced into circulation in the reactor 2.) similarly to the flow 20.

In the light of everything described above, it is therefore possible to summarise here some of the characteristic aspects of the present invention as follows.

[1] An apparatus for the mineralization of carbon dioxide in the forms of solid carbonates of a precursor material comprising at least one of alkali metals, alkaline earth metals, transition metals and carbonated synthetic carbonate materials, said apparatus comprising at least: a loading device (1) of a mixture of the precursor material and water; a reactor (2) equipped with a plurality of inlet and/or outlet openings for the introduction of the mixture of the precursor material and water or processing wastewater, and for the emission of an aqueous suspension of the precursor; a cavitation device (5) placed externally to said reactor and in fluid connection therewith, said cavitation device (5) being placed along a recirculation circuit originating and flowing into the reactor (2); at least one device (7, 10,18), at the exit from said reactor (2), for the separation of the reaction products and the recovery of the wastewater; in which there is at least one injection point (4a, 4b, 4c) of a gaseous mixture containing, or consisting of, CO2 placed upstream of the cavitation device (5).

[2] An apparatus in accordance with what is described in the previous point [1], in which said cavitation device (5) consists of one or more cavitation elements, of static and/or dynamic type, and/or in which said cavitation device (5) comprises at least one passive cavitator, or at least one active cavitator, or a plurality of cavitators comprising at least one passive cavitator and at least one active cavitator, and/or in which said cavitation device (5) comprises at least one passive cavitator and at least one active cavitator, where the passive cavitator is placed upstream of the active cavitator.

[3] An apparatus in accordance with what is described in the previous points [1] or [2], in which the at least one injection point (4a, 4b, 4c) of a gaseous mixture containing, or consisting of, CO2 is placed in the reactor (2) and/or outside the reactor (2) upstream of a pump (3) for intercepting said aqueous suspension of the precursor and/or downstream of the interception pump (3) and upstream of the cavitation device (5).

[4] An apparatus in accordance with any one of the preceding points, further comprising an oxygenator element (24), preferably a serpentine element, placed along the recirculation circuit upstream of the cavitation device (5), in which the injection point (4a, 4b, 4c) of the gaseous mixture containing, or consisting of, CO2 is placed upstream of said oxygenator element (24).

[5] An apparatus according to any one of the preceding points, in which said at least one device (7,10,18) for the separation of reaction products and for the recovery of wastewater is selected from a hydro-cyclone separator and/or a settler and/or a sedimentation chamber and/or a flotation chamber and/or a bag and/or a tank and/or a drainage belt and/or a centrifuge and/or a filter press.

[6] An apparatus in accordance with any one of the preceding points, in which said loading device (1) is a hopper or any functional analogue thereof known in the art.

[7] An apparatus in accordance with any one of the preceding points, in which the feeding of the mixture of precursor material and water occurs and is controlled by means of a device such as a rotary valve, or an auger, or any functional analogue thereof known in the art.

[8] An apparatus in accordance with any one of the preceding points, in which said precursor is selected from waste/slag such as steel mill slag, basic industrial sludge from civil and industrial effluents, from paper mills, from alumina, zinc or titanium dioxide treatment processes (red sludge), from fly ash from incineration.

[9] An apparatus in accordance with what is described in any one of the preceding points, further comprising at least:

- a collection tank (21), outside the reactor (2), configured to contain a liquid enriched in alkali coming from a separation step of said liquid from the partially carbonated precursor; and

- a gas abatement tower (23) or scrubber, for the formation of solid carbonates from said liquid enriched in alkali after treatment with a flow of a gaseous stream containing, or consisting of, CO₂.

[10] Process for the mineralization of carbon dioxide in the forms of solid carbonates of a precursor material comprising at least one of alkali metals, alkaline earth metals, transition metals and possible carbonated synthetic carbonate materials, comprising at least the following steps: a) loading a suspension of said precursor material in water into a reactor (2) by means of a loading device (1), through a first opening of the reactor (la); b) intercepting, through a second opening of the reactor (lb), said aqueous suspension of the precursor by means of a pump (3) and pumping it through a cavitation device (5), together with a gaseous stream containing, or consisting of, CO2 fed to the aqueous suspension of the precursor upstream of the cavitation device (5); c) reintroducing into the reactor, through a third opening (1c) thereof, the flow in output from said cavitation device (5) and continuing the cycle of the cavitation process until a desired pH is obtained in the reactor.

[11] The process for the mineralization of carbon dioxide in accordance with what is described in the preceding point [10], further comprising at least one of the following steps: d) sending, through a fourth opening (Id) of the reactor, by means of a pump (6), a suspension resulting from step c) into a first separation device (7) and separating the components of said suspension to give, respectively, a final solid (consisting of carbonates and carbonated precursor) and wastewater, or a partially carbonated solid and a liquid enriched in alkali; and/or e) discharging a residual content at the bottom of the reactor (2) through a further opening (1g) on the bottom thereof into a further separation device (10) and separating the components to give a sludge flow (11) and a wastewater flow (12).

[12] The process for the mineralization of carbon dioxide in accordance with what is described in the preceding point [11], further comprising at least the following steps: f) transferring, by means of a pump (22), the aforesaid liquid enriched in alkali from a collection tank (21) to a gas abatement tower or scrubber (23), where the liquid enriched in alkali is first atomized and then hit by a gaseous stream containing, or consisting of, CO2 to give a suspension of water and solid carbonates; and g) transferring, by means of a pump (16), said suspension of water and solid carbonates into a second separation device (18) and separating the components of said suspension to give a final solid (consisting of solid carbonates) (19) and wastewater (20).

[13] The process for the mineralization of carbon dioxide in accordance with what is described in any one of the preceding points from [10] to [12], in which the gaseous flow containing, or consisting of, CO2 fed to the aqueous suspension of the precursor upstream of the cavitation device (5) is fed directly into the reactor (2), and/or externally to the reactor (2) upstream of said precursor aqueous suspension interceptor pump (3) and/or downstream of said interceptor pump (3) and upstream of said cavitation device (5).

[14] The process for the mineralization of carbon dioxide in accordance with what is described in any one of the preceding points from [10] to [13], in which the step of pumping the aqueous suspension of the precursor through a cavitation device (5) comprises pumping the aqueous suspension of the precursor first through a passive cavitator and then through an active cavitator located downstream of the passive cavitator.

[15] The process for mineralization of carbon dioxide in accordance with what is described in any one of the preceding points from [10] to 14, in which the step of pumping the aqueous suspension of the precursor through a cavitation device (5) comprises passing the aqueous suspension of the precursor through an oxygenator element (24), preferably a serpentine element, located upstream of the cavitation device (5), in which the gaseous stream containing, or consisting of, CO2 is fed to the aqueous suspension of the precursor upstream of the oxygenator element (24).

In all the preferred embodiments of the process of the present invention, advantageously the cavitation device: maximizes the solubility of carbon dioxide in solution; maximizes mass transfer from the precursor to the solution; intensifies the reactivity of the species involved; renews the reactive surface of the precursor by means of the phenomenon of cavitation and thus maximizes the overall release of the reactive material to the carbon dioxide.

Furthermore, by sending a gaseous stream containing, or consisting of, carbon dioxide through the cavitation device at the same time as the precursor-water suspension, an effect of increased release of carbonatable material from the precursor to the aqueous phase is achieved.

In the third preferred embodiment of the process of the present invention, the transfer of the reactive elements contained in the precursor to the liquid phase is advantageously maximized, which is then treated separately in a dedicated additional element (the scrubber). Advantageously, this thereby potentially maximizes the amount of pure carbonates obtained.

Furthermore, in the first embodiment of the invention, the final product is a mixture of reacted precursor (i.e., carbonated) and carbonates, which can be separated later.

In the third embodiment, the end products are a carbonate flow and a flow consisting of unreacted, or only partially carbonated, treated precursor.

With respect to the direct CO2 pumping technologies of the known art (mentioned above), advantageously, the equipment and related processes of the invention tend to remove carbonaceous substances, avoiding fouling in the system. In particular, the effect of cavitation has proved to be crucial in achieving this type of result.

Furthermore, advantageously, in the preferred embodiments of the present invention, a particle size control element is not required.

In fact, particle size control depends on the physics of cavitation itself: the cavitation bubbles formed close to the surfaces of the precursor materials have a very short life (from a few ms to a few tens of ms), after which they implode, causing an increase in pressure inside the bubble which leads to the formation of a real plasma; their implosion fragments the surfaces of the granules, reducing them to mini-fragments of the order of a few tens of nm, preferably between 10 and 100 nm. The nanoscopic fragments thus obtained then crystallize rapidly in the form of carbonates.

The benefits of the innovative technology provided by the present invention are many, such as:

1) The precursor is maximally consumed and the conditions for the passivation of the material are not created;

2) Carbon dioxide is maximally solubilized by the effects of the cavitator action;

3) No fouling conditions are created; in fact, the system remains clean;

4) The system can also (preferably) be used in continuous production.

In conclusion, all the details are substitutable by other technically equivalent elements; the materials used, as well as the contingent shapes and dimensions, which may be any according to the specific implementation requirements without departing from the scope of protection of the following claims.

Claims

1. Apparatus for the mineralization of carbon dioxide in the forms of solid carbonates of a precursor material comprising at least one of alkali metals, alkaline earth metals, transition metals and carbonated synthetic carbonate materials, the apparatus comprising at least: a loading device (1) of a mixture of the precursor material suspended in water;

- a reactor (2) equipped with a plurality of inlet and/or outlet openings for the introduction of the mixture of the precursor material suspended in water and/or processing wastewater, and for the emission of an aqueous suspension of the precursor;

- a cavitation device (5) placed externally to said reactor and in fluid connection therewith, the cavitation device (5) being positioned along a recirculation circuit originating and flowing into the reactor (2);

- at least one device (7,10,18), at the exit from said reactor (2), for the separation of reaction products and the recovery of processing wastewater; wherein at least one injection point (4a, 4b, 4c) of a gaseous mixture containing, or consisting of, CO2 is provided upstream of the cavitation device (5).

2. Apparatus according to claim 1, wherein said cavitation device (5) consists of one or more cavitation elements, of static and/or dynamic type, and/or wherein said cavitation device (5) comprises at least one passive cavitator, or at least one active cavitator, or a plurality of cavitators comprising at least one passive cavitator and at least one active cavitator, and/or wherein said cavitation device (5) comprises at least one passive cavitator and at least one active cavitator, where the passive cavitator is placed upstream of the active cavitator.

3. Apparatus according to claim 1 or 2, wherein the at least one inj ection point (4a, 4b, 4c) of a gaseous mixture containing, or consisting of, CO2 is placed in the reactor (2) and/or outside the reactor (2) upstream of a pump (3) for intercepting said aqueous suspension of the precursor and/or downstream of the interception pump (3) and upstream of the cavitation device (5).

4. Apparatus according to any one of the preceding claims, further comprising an oxygenator element (24), preferably in the form of a coil, placed along the recirculation circuit upstream of the cavitation device (5), wherein the injection point (4a, 4b, 4c) of the gaseous mixture containing, or consisting of, CO2 is placed upstream of the oxygenator element (24).

5. Apparatus according to any one of the preceding claims, wherein the at least one device (7,10,18) for separating reaction products and for recovering processing wastewater is selected from the group consisting of: a hydrocyclone separator, a settler, a flotation chamber, a bag, a tank, a drainage belt, a centrifuge and a filter press.

6. Apparatus according to any one of the preceding claims, wherein said loading device (1) is a hopper or any functional analogue thereof.

7. Apparatus according to any one of the preceding claims, wherein the feeding of the mixture of precursor material suspended in water occurs and is controlled by means of a device such as a rotary valve, or a cochlea, or any functional analogue thereof.

8. Apparatus according to any one of the preceding claims, wherein said precursor is selected from wastes/slags such as steel mill slag and/or basic industrial sludge from civil and industrial wastewater and/or from paper mills and/or from alumina and/or zinc and/or titanium dioxide treatment processes (red sludge) and/or from incineration fly ash.

9. Apparatus according to any one of the preceding claims, further comprising at least:

10. Process for the mineralization of carbon dioxide in the forms of solid carbonates of a precursor material comprising at least one of alkali metals, alkaline earth metals, transition metals and possible carbonated synthetic carbonate materials, comprising at least the following steps: a) loading a suspension of the precursor material in water into a reactor (2) by means of a loading device (1), through a first opening of the reactor (la); b) intercepting, through a second opening of the reactor (lb), said aqueous suspension of the precursor by means of a pump (3) and pumping it through a cavitation device (5), together with a gaseous stream containing, or consisting of, CO2 fed to the aqueous suspension of the precursor upstream of the cavitation device (5); c) reintroducing into the reactor, through a third opening (1c) thereof, the flow in output from said cavitation device (5) and continuing the cycle of the cavitation process until a desired pH is obtained in the reactor.

11. The process for the mineralization of carbon dioxide according to claim 10, further comprising at least one of the following steps: d) sending, through a fourth opening (Id) of the reactor, by means of a pump (6), a suspension resulting from step c) into a first separation device (7) and separating the components of said suspension to give, respectively, a final solid (consisting of carbonates and carbonated precursor) and wastewater, or a partially carbonated solid and a liquid enriched in alkali; and/or e) discharging a residual content at the bottom of the reactor (2) through a further opening (1g) on the bottom thereof into a further separation device (10) and separating the components to give a sludge flow (11) and a wastewater flow (12).

12. The process for the mineralization of carbon dioxide according to claim 11, further comprising at least the following steps: f) transferring, by means of a pump (22), the aforesaid liquid enriched in alkali from a collection tank (21) to a gas abatement tower or scrubber (23), where the liquid enriched in alkali is first atomized and then hit by a gaseous stream containing, or consisting of, CO2 to give a suspension of water and solid carbonates; and g) transferring, by means of a pump (16), said suspension of water and solid carbonates into a second separation device (18) and separating the components of said suspension to give a final solid (consisting of solid carbonates) (19) and wastewater (20).

13. The process for the mineralization of carbon dioxide according to any one of claims 10 to 12, wherein the gaseous stream containing, or consisting of, CO2 fed to the aqueous suspension of the precursor upstream of the cavitation device (5) is fed directly into the reactor (2), and/or outside the reactor (2) upstream of the interception pump (3) of said aqueous suspension of the precursor and/or downstream of the interception pump (3) and upstream of the cavitation device (5).

14. The process for the mineralization of carbon dioxide according to any one of claims 10 to 13, wherein the step of pumping the aqueous suspension of the precursor through a cavitation device (5) comprises pumping the aqueous suspension of the precursor first through a passive cavitator and then through an active cavitator located downstream of the passive cavitator.

15. The process for the mineralization of carbon dioxide according to any one of claims 10 to 14, wherein the step of pumping the aqueous suspension of the precursor through a cavitation device (5) further comprises passing the aqueous suspension of the precursor through an oxygenator element (24), preferably in the form of a coil, located upstream of the cavitation device (5), wherein the gaseous flow containing, or consisting of, CO2 is fed to the aqueous suspension of the precursor upstream of the oxygenator element (24).

16. The process for the mineralization of carbon dioxide according to any one of claims 10 to 14, wherein the precursor material in addition comprises a suitable additive to make the reaction process more efficient with the gaseous flow containing, or consisting of, CO2, wherein the additive is preferably sodium hydroxide (NaOH).