Method for forming carbon-negative minerals using biomineralising macroorganisms

Abstract

The invention relates to a method for producing a carbon-negative biomineralised macroorganism, the method comprising the following steps: providing a biomineralising macroorganism comprising an organic phase and a mineral phase containing calcium carbonate; culturing the biomineralising macroorganism, in an atmosphere comprising carbon dioxide, in a culture solution comprising salt water having a salinity of between 3 and 260 PSU and an alkalinity of between 1 mmol / L and 200 mmol / L, wherein, during the culturing step, the biomineralising macroorganism produces calcium carbonate crystals; adding an alkaline feedstock to the culture solution in order to ensure the growth of the calcium carbonate crystals of the biomineralising macroorganism during its biomineralisation; harvesting at least part of the biomineralised macroorganism when one of its average dimensions is greater than or equal to 1 cm.

Description

[0001] PROCESS FOR FORMING CARBON-NEGATIVE MINERALS USING BIOMINERALIZING MACROORGANISMS

[0002] Technical field of the invention

[0003] The invention relates to the production of biomineralized macroorganisms having a negative carbon footprint, as well as the use of such macroorganisms in a composition of a construction material.

[0004] Technological background

[0005] In the context of the present invention, a macroorganism is a living organism, animal or plant, composed of several cells, to be distinguished from unicellular microorganisms such as bacteria, cyanobacteria or microalgae.

[0006] For the purposes of this invention, a biomineralized macroorganism is defined as a macroorganism capable of producing inorganic minerals through biological processes. These inorganic minerals are often used to form structures such as shells or skeletons, for example.

[0007] By negative carbon footprint, or carbon negative, in the sense of the present invention, it is understood that the process of producing biomineralized macroorganisms removes more carbon dioxide (CO2) from the atmosphere than it emits.

[0008] In what follows, we focus in particular on the materials used in the manufacture of concrete to reduce its carbon footprint, although the invention can be applied to other construction materials, such as mortar, paint, or even in the composition of materials for earthworks, this list is not exhaustive.

[0009] Concrete production involves the use of cement, which primarily uses a fired material called clinker. Clinker is obtained from a raw material composed of several minerals, including clay, a source of aluminosilicates, and limestone, a source of calcium carbonate. Typically, these minerals are successively mixed, dried, ground, preheated, decarbonated, and then fired before being partially melted in a rotary kiln to a temperature of approximately 1500°C. Finally, the resulting clinker is cooled. In the clinker manufacturing process, in addition to greenhouse gas emissions such as carbon dioxide (CO2) from the combustion of the fuels used, CO2 is emitted when the calcium carbonate, mainly derived from limestone, is decarbonated to produce lime, which is a cementing agent.It should be noted that lime is capable of recombining with silicon, aluminum, and iron oxides in the rotary kiln to form clinker. This decarbonation process releases a significant amount of carbon dioxide, at least some of which is conventionally released into the atmosphere, thus contributing to climate change. This is why national legislation regarding carbon dioxide emissions is becoming stricter, requiring clinker manufacturers, in particular, to reduce the amount of carbon dioxide released.

[0010] Cement, on the other hand, is obtained by finely grinding a mixture composed mainly of clinker. Cement also contains gypsum, which helps regulate the setting time of construction materials such as mortars and concretes made from cement.

[0011] Cement also increasingly contains, and in increasing proportions, clinker substitute materials commonly called "cement additions" which replace part of the clinker in order to reduce the environmental impact, in particular the carbon footprint, and possibly the cost associated with cement production.

[0012] For example, the most commonly used clinker substitutes today are blast furnace slag, fly ash from coal-fired power plants, natural pozzolan, and limestone, which is generally ground into a fine powder before being incorporated into the clinker. It should be noted that these clinker substitutes have pozzolanic reactivity, allowing them to participate in the hydraulic setting reaction. This pozzolanic reactivity helps maintain the desired mechanical properties of construction materials, which primarily consist of cement and sand, even as the clinker content decreases.

[0013] Indeed, limestone is a good candidate as a substitute for clinker, then referred to as "limestone filler" or "limestone aggregate," due to its low carbon footprint and sufficient availability in nature. However, it should be noted that the carbon footprint of limestone is not zero, specifically approximately 75 kg CO2 / tonne of limestone, given that no energy source is entirely carbon-free, and considering the amount of energy used to extract, transport, and crush it.

[0014] However, other techniques exist that complement or replace those mentioned above in order to further reduce the carbon footprint of cement. For example, there is the technique known as "CarbonCure," which involves injecting liquefied carbon dioxide during cement production. This notably improves the strength of the concrete produced later. Indeed, some of the lime produced during clinker manufacturing, called free lime, which is ultimately contained in the cement, reacts with the injected carbon dioxide to form calcite. This carbon dioxide is then permanently sequestered in the resulting concrete.This technique, which only applies to prestressed concrete, however, does not constitute a solution defined by a negative carbon footprint, in particular due to the necessary presence of lime in the clinker whose production process inevitably releases as much carbon dioxide into the atmosphere as is trapped.

[0015] It is also known that techniques are used to incorporate carbonate materials, particularly calcium carbonate, derived from the biomineralization of cultured microorganisms, into a concrete or mortar composition. Examples of microorganisms include microalgae such as coccolithophores, bacteria such as ureolytic bacteria, and cyanobacteria.

[0016] However, to produce carbonate materials from ureolytic bacteria, an amendment of urea is required, but urea has a high carbon footprint, approximately 3 tonnes of carbon dioxide per tonne of urea.

[0017] More generally, to produce carbonate materials from microalgae or bacteria, high quantities of nutrients and vitamins are typically added to the culture solution, even though these nutrients and vitamins have significant positive carbon footprints. Furthermore, currently known biologically formed calcium carbonates are not carbon negative.

[0018] Thus, current techniques remain improvable and there is, in particular, a need to produce carbonate materials, especially calcium carbonate, defined by negative carbon footprints, for use in cement compositions as a limestone filler.

[0019] Objectives of the invention

[0020] The present invention proposes a method for producing calcium carbonate from the culture of at least one macroorganism capable of biomineralizing to produce calcium carbonate crystals. This macroorganism is then referred to as calcifying. The biomineralized macroorganism produced has a negative carbon footprint due to its culture conditions.

[0021] Description of the invention

[0022] To this end, the invention relates to a method for producing a carbon-negative biomineralized macroorganism, the method comprising the following steps: a) supplying a biomineralizing macroorganism comprising an organic phase and a mineral phase containing calcium carbonate, b) culturing, under an atmosphere comprising carbon dioxide, the biomineralizing macroorganism in a culture solution comprising salt water having a salinity level between 3 and 260 PSU and an alkalinity level between 1 mmol / L and 200 mmol / L, culture during which the biomineralizing macroorganism, during its biomineralization, produces calcium carbonate crystals, c) adding an alkaline charge to the culture solution to maintain the alkalinity level of the culture solution between 1 mmol / L and 200 mmol / L and ensure the growth of the carbon-negative calcium carbonate crystals of the biomineralizing macroorganism during its biomineralization,d) harvesting at least part of the biomineralized macroorganism when one of its average dimensions is greater than or equal to 1 cm.

[0023] Such a process has a negative carbon footprint insofar as the total carbon dioxide emissions linked to the energy consumption of the culture system, which is essentially linked to lighting, heating and pumping, are significantly lower than the amount of carbon dioxide that can be sequestered by these biomineralized macroorganisms.

[0024] The mineral phase of the biomineralized macroorganism consists of calcium carbonate and is formed from carbon dioxide captured from the atmosphere, either directly by the biomineralizing macroorganism through photosynthesis, or by the culture solution in which the carbon dioxide dissolves as inorganic carbon through the addition of an alkaline charge. This process does not require the introduction of any nutrients and / or vitamins into the salt-based culture solution, such as seawater, which contributes to the process's negative carbon footprint.

[0025] It is also worth noting that the biomineralizing macroorganism supplied in step a) of the supply process is either autotrophic and photosynthetic, fixing carbon dioxide, or heterotrophic, meaning it consumes carbon dioxide-fixing organisms. In each case, the organism sequesters carbon dioxide directly or indirectly by producing the organic matter of which it is partially composed. This, in addition to the calcium carbonate biomineralization processes, contributes to reducing the carbon footprint of this cultivation method.

[0026] This biomineralizing macroorganism is calcifying, meaning it produces calcium carbonate crystals during its growth. These crystals are harvested in step d) when the organism reaches a sufficiently large size. It should be noted that no complex filtration methods are required during this step. Furthermore, the biomineralizing macroorganism is domesticable, meaning that it can be removed from its natural environment and grows sufficiently when cultivated.

[0027] Advantageously, the culture solution in step b) above has a pH between 6 and 10, under a light intensity between 1 and 2200 pmol / m³ 2 / s, and a temperature between 0 and 55°C.

[0028] Advantageously, step c) of adding an alkaline load to the culture solution is carried out at an addition frequency at a given concentration which is dependent on the growth rate of the supplied biomineralizing organism and taking into account that the pH of the solution must be maintained between 6 and 10.

[0029] Preferably, the biomineralizing macroorganism supplied in step a) is chosen from the group consisting of corals, macroalgae, bryozoans or a mixture of the aforementioned macroorganisms.

[0030] Such biomineralizing macroorganisms have the particularity of growing relatively rapidly in a culture solution that is in contact with an atmosphere containing carbon dioxide, and require lower quantities of nutrients, for equivalent biomass produced, compared to calcareous microorganisms such as coccolithophores. For example, corals include Accropora, Porites, Stylophora, Seriatopora, Cyphastrea, Pocillopora, Hydnophora, Heliopora, and Montipora.

[0031] For example, bryozoans include Cellaria, Reteporella, and Pentapora.

[0032] Preferably, the biomineralizing macroorganism is a macroalga.

[0033] For example, macroalgae include Jania, Galaxaura, Halimedaceae, Corallinophycidae, and Dichotomaria.

[0034] Preferably, the macroalga is chosen from the order Bryopsidales, in particular the family Halimedaceae, and in particular the genus Halimeda.

[0035] Halimeda has the advantage of a high growth rate, even in culture medium. Furthermore, it is relatively tolerant of different environmental conditions, particularly varying alkalinity levels, but also relatively high concentrations of trace metals, which allows it to be cultivated in culture solutions fed with industrial and / or mining waste.

[0036] It is also worth noting that, during stage b) of the culture, the carbon dioxide content of the salt water near the macroorganism decreases, which triggers a decrease in the carbon dioxide content of the atmosphere near the culture solution. Specifically, the carbon dioxide removed from the atmosphere is transformed and then stored in the mineral phase of the biomineralized macroorganism. Such storage is considered sustainable, even permanent, since the calcium carbonate that constitutes the mineral phase, without human intervention, is able to sequester the stored carbon dioxide for over 1000 years without it being released into the atmosphere.

[0037] In particular, step b) of the culture optimizes the diffusion kinetics of carbon dioxide from the atmosphere to the culture solution, and then from the culture solution to the biomineralizing macroorganism, through the continuous consumption of inorganic carbon dissolved in the culture solution by the biomineralizing macroorganism during its biomineralization. For example, the culture solution can be a renewable marine resource, such as seawater, in which the biomineralizing macroorganism is at least partially submerged. It should be noted that the culture solution can be either an artificial solution, a natural solution, or a mixture of an artificial and a natural solution. Preferably, the salinity of the culture solution is between 31 and 39 PSU and the alkalinity of the culture solution is between 1 and 20 mmol / L.

[0038] Preferably, step b) of cultivation is implemented under natural lighting conditions or under artificial lighting conditions using white LED lamps.

[0039] Preferably, during step b) of culture, the biomineralizing macroorganism is placed on a substrate consisting of sand and / or rock fragments, or rope.

[0040] For the purposes of this invention, rope means a system of ropes immersed in salt water serving as a support on which the macroorganism can attach itself.

[0041] Preferably, the substrate is similar to the substrate of the natural living environment of the cultivated biomineralizing macroorganism.

[0042] In one particular case, the process further includes a step of injecting a concentrated carbon dioxide gas into the culture solution during step b) of the culture. This further promotes the continuous consumption of inorganic carbon dissolved in the culture solution by the biomineralizing macroorganism during its biomineralization. For example, the concentrated gas can be obtained from prior carbon dioxide capture from any type of industry or directly from the air.

[0043] Furthermore, step c) of adding an alkaline charge to the culture solution ensures a geochemical equilibrium between the culture solution and the atmosphere. This prolongs the dissolution of atmospheric carbon dioxide in the culture solution and ensures the sequestration of inorganic carbon, initially contained in the culture solution and subsequently in the biomineralizing macroorganism during its biomineralization process.

[0044] For example, as an alkaline load, we can cite alkaline rocks such as volcanic ash, pozzolana, peridotite, basalt, divines or materials generated as by-products of waste in industry such as recycled cement, cement kiln dust (commonly referred to by the English acronym "CKD"), concrete waste, sodium carbonate and bicarbonate waste, or mining waste.

[0045] It should be noted that the alkaline feedstock added in step c) is preferably waste or collected from the environment. This allows for the use of renewable alkaline resources, resulting in a more economical and environmentally friendly process. For example, the alkaline feedstock can be collected as waste, industrial and / or mining by-products, or directly from a naturally concentrated source of alkaline elements.

[0046] Thus, according to the process of the invention, carbon-negative biominerals are formed under conditions different from those inherent in natural seawater. As such, the carbon-negative biominerals thus formed from the biomineralized macroorganism produced according to the invention are defined by a chemical composition different from that defining biominerals formed under natural conditions, particularly in seawater. For example, the isotopic composition of boron (β₂O) differs from that of biominerals formed under natural conditions, particularly in seawater. 11 B), combined with their Boron / Calcium ratio, carbon-negative biominerals thus formed according to the invention is significantly different from that of biominerals formed under natural conditions.

[0047] Furthermore, it is known that biominerals formed under natural conditions contain, depending on the natural sources of alkalinity in which they grow and which are more or less rich in metals, quantities of trace elements incorporated in their different carbonates which, in proportion, are much lower than those contained in biominerals formed from the biomineralized macroorganism produced according to the invention.

[0048] Furthermore, according to the invention, calcium carbonate crystals grow using, in particular, inorganic carbon dissolved in the culture solution in equilibrium with atmospheric carbon dioxide, and the radiocarbon composition can be measured 14 C / 12 This 14 C / 13 The calcium carbonate content in the biomineralized macroorganism produced according to the process of the invention may attest to a recent (and not fossil) source of CO2.

[0049] The invention also relates to a carbon-negative biomineralized macroorganism produced by implementing a process as described above, containing calcium carbonates of an aragonitic nature.

[0050] The invention also relates to a method for manufacturing, at least from the biomineralized macroorganism as described above, a carbon-negative powder for a construction material composition. The method optionally includes a step e) of drying the biomineralized macroorganism, followed by a step f) of first grinding the biomineralized macroorganism to obtain ground biomineral particles defined by a first average particle size between 5 µm and 500 µm and an organic fraction initially contained in the biomineralized macroorganism. Step f) of first grinding, referred to as coarse grinding, is less energy-intensive than fine grinding, but nevertheless allows the organic phase of the biomineralized macroorganism to be readily accessible for subsequent processing.

[0051] The manufacturing process may further include a step g) of separating the organic fraction and biomineral particles by a physical and / or chemical operation.

[0052] This separation step (g) can preferably be carried out by a sieving step (g1) to obtain biomineral particles separated from the organic fraction. This sieving is said to be precise. Preferably, it allows the separation of the organic fraction containing organic particles defined by a high average particle size, typically greater than or equal to 100 µm, which is coarser in terms of particle size than the inorganic phase consisting of biomineral particles defined by a low average particle size, typically less than or equal to 100 µm, which is finer.

[0053] Preferably, separation step g) may include a step g2) of heating the biomineral particles to a temperature between 400°C and 600°C, or even to a temperature between 250°C and 400°C. Such heating induces combustion of the organic fraction while preventing combustion of the biomineral particles. It should be noted that the carbon dioxide produced by this combustion can be captured subsequently, for example, by injecting it into the culture solution for reuse as a carbon dioxide source and for subsequent sequestration by the biomineralizing macroorganisms during its biomineralization.

[0054] Step g) of this separation process may also include a further step g3) of contacting the biomineral particles with a solution comprising sodium hypochlorite, sodium hydroxyl, hydrogen peroxide, or a mixture of the aforementioned elements. The purpose of this is to digest the organic fraction by oxidation. Similarly, the carbon dioxide produced by this oxidative digestion can be captured subsequently, for example, by injecting it into the culture solution for reuse as a carbon dioxide source, to be sequestered again by the biomineralizing macroorganisms during its biomineralization.

[0055] Step g1, step g2, or step g3 removes the remaining organic fraction from the biomineral particles. In this way, the resulting biomineral particles meet the total organic carbon content defined by cement standard 197-1, allowing them to be used as a limestone filler or aggregate. For the purposes of this invention, average particle size refers to the average size of the biomineral particles produced.

[0056] Preferably, the process further includes a step h) of a second grinding until ground biomineral particles are obtained, defined by an average particle size between 5 µm and 90 µm. This makes it possible to obtain biomineral particles defined by an average particle size below the threshold determined by standard NF EN 196-6.

[0057] In this way, such a powder can be directly incorporated into a clinker composition as a limestone filler. This reduces the dependence of cement compositions on non-renewable resources and minimizes the carbon footprint associated with the conventional manufacturing of cement components.

[0058] Furthermore, this powder offers specific compressive strength, active properties in cement, and hydraulic properties in concrete at least equivalent to limestone, which is currently used in clinker compositions to reduce their carbon footprint. Additionally, this powder contains euhedral crystals that can promote aragonite formation when the free lime in the cement reacts naturally with atmospheric carbon dioxide and precipitates as calcium carbonate.

[0059] Brief description of the figures

[0060] Other features and advantages of the invention will now become apparent in greater detail in the following description of illustrative and non-limiting embodiments, with reference to the attached figures which represent:

[0061] - Figure 1 represents an image obtained by Scanning Electron Microscopy (SEM) at X2050 magnification of calcium carbonate crystals of negative carbon biomineral particles from the process described in Example 1 which is a process according to an embodiment of the invention;

[0062] - Figure 2 shows a Scanning Electron Microscopy (SEM) image at 15,760x magnification of carbon-negative calcium carbonate crystals produced by the process described in Example 1; - Figure 3 shows a Scanning Electron Microscopy image at 329x magnification (left image), equipped with an EDX elemental probe, of a cement paste comprising a carbon-negative powder obtained according to an embodiment of the invention. The image at the top right shows the surface distribution of calcium (light shade), representing the distribution of the calcium carbonate filler within the cement paste. The image at the bottom right shows the surface distribution of silicon (light shade), representing the distribution of the cement powder within the cement paste;

[0063] - Figure 4 represents an image obtained by Scanning Electron Microscopy at 894x magnification (left image), equipped with an EDX elemental probe, of a cement paste from a prior art. The image at the top right represents the surface distribution of calcium (light shade), reflecting the distribution of the calcium carbonate filler within the cement paste. The image at the bottom right represents the surface distribution of silicon;

[0064] - Figure 5 represents a cathodoluminescence image of a cement paste comprising a negative carbon powder obtained according to an embodiment of the invention;

[0065] - Figure 6 represents an image obtained by cathodoluminescence of a cement paste from an earlier art;

[0066] - Figure 7 schematically describes the (bio)chemical reactions associated with each step of the process of CO2 capture, seawater alkalization, and biomineralization and possibly photosynthesis;

[0067] - Figure 8 represents the evolution of the cumulative increase in alkalinity in mmol / l in the culture solution during a capture and mineralization sequence (time bar 1) representing the start date of addition (Day 16) of it at 0.13 mmol / l / day, time bar 2) representing the start date of addition (Day 24) of it at 0.30 mmol / l / day);

[0068] - Figure 9 shows the evolution of the Ca concentration 2+ in parts per million (ppm) in the culture solution during the experiment (both time bars are similar to those in Figure 8);

[0069] Figure 10 shows the evolution of the total alkalinity concentration in mmol / l in the culture solution during the experiment (the two time bars are similar to those in Figure 8). Examples

[0070] The present invention will be better understood by reading the following examples which illustrate the invention in a non-limiting way.

[0071] Example 1: Example of a process for producing carbon-negative biomineral particles obtained from a carbon-negative biomineralized macroorganism according to an embodiment of the invention:

[0072] The macroorganism Halimeda opuntia is cultured in an aquarium heated to 26°C in a culture medium consisting of salt water with a salinity of approximately 35 PSU and an alkalinity between 2.8 and 3.2 mmol / L. The alkalinity of the culture medium is maintained at these values ​​by adding alkalinity to the culture medium and to a sandy substrate. For example, this alkalinity can be added to the culture medium by adding slaked lime (calcium hydroxide; Ca(OH)2) from a production site where CO2 emissions are captured at the source, or from cement waste, or waste from soda ash production. Multi-centimeter fragments of several sufficiently large individual biomineralized macroorganisms were collected without compromising their survival. A total of 4.0 grams of these fragments was ground using an agate mortar and pestle (99.9% SiO2), whose very fine structure prevents any contamination of the fragments by the mortar during grinding. This allows for the production of biomineral particles with an average particle size ranging from 5 µm to 500 µm. A first step of separating the organic fraction from the ground biomineral particles is carried out in a 3% hydrogen peroxide bath for 12 hours to dissolve the least refractory organic matter in the biomineral particles and obtain biomineral particles separated from this less refractory organic matter. This step is followed by rinsing the biomineral particles separated from the least refractory organic matter with demineralized water, and then air-drying them for 24 hours.This step is followed by a sieving step to separate the biomineral particles from the less refractory organic matter, leaving behind the more refractory residual organic fraction with an average particle size greater than 100 µm. This yields biomineral particles that are virtually free of all organic fractions. These biomineral particles are then ground again to achieve the finest possible particle size, ideally less than 100 µm. As an alternative or complement to the aforementioned sieving step, the organic fraction can be separated from the biomineral particles by means of a heat treatment, for example, heating at a temperature between 400 and 600°C, or even between 250 and 600°C.

[0073] As an alternative or complement, the separation of the organic fraction from the biomineral particles is carried out by means of a chemical oxidation of the organic matter.

[0074] It is therefore possible to use either sieving, heating, chemical oxidation of organic matter, or a combination of at least two of these techniques, to isolate the mineral phase from the organic matter.

[0075] The ground biomineral particles correspond, as illustrated in Figure 1, to calcium carbonate crystals agglomerated into agglomerates whose average size is generally less than 100 pm, or, as illustrated in Figure 2, individualized micrometric or sub-micrometric.

[0076] Example 2: Example of making a cement paste including the powder obtained according to example 1

[0077] The ground biomineral particles obtained according to Example 1 are mixed with CEM1 cement in mass proportions such that the biomineral particles represent 30% of the mixture and the CEM1 70%. Water is added to the mixture to make up 33% of the final mixture to obtain a cement paste. This cement paste is then molded in silicone molds to produce, after air drying, bricks with a cross-sectional dimension of several centimeters.

[0078] Fragments of these bricks are then polished using polishing paper to obtain the smoothest possible surfaces necessary for scanning electron microscopy (SEM) imaging (figure 3) and cathodoluminescence imaging (figures 5).

[0079] The EDX probe allows semi-quantitative chemical analysis illustrating the surface distribution of calcium (map at top right of figure 3) which traces the phases rich in calcium carbonates (limestone filler') and of silicon (map at bottom right of figure 3) which traces the cement phases.

[0080] Comparative example: example of a cement paste obtained using a prior art process. An industrial limestone filler (Betocarb® F-SL, SALSES, France, certified ISO 9001, 14001 and OHSAS 18001, category A-Fh according to standard NF P 18-508) made of micrometric calcium carbonate particles from limestone quarries is mixed with CEM1 cement in mass proportions such that the carbonate particles represent 30% of the mixture and the CEM1 70%. Water is added to the mixture to make up 33% of the final mixture to obtain a cement paste using a prior art process. This cement paste is then molded in silicone molds to produce, after air drying, bricks with a cross-sectional dimension of several centimeters.

[0081] Comparisons and results:

[0082] Using Figures 3 and 4, it can be seen that the carbonate phase of the powder is distributed homogeneously in a cement paste comprising biomineral particles obtained according to the invention, similarly to that in the case of a state-of-the-art cement paste (obtained according to the comparative example).

[0083] Furthermore, Figures 5 and 6, obtained by cathodoluminescence, illustrate the results of different crystallographic processes during the setting of the cement paste containing the biomineral particles obtained according to the invention, compared to the setting with a limestone filler contained in the cement paste obtained according to the aforementioned comparative example. In particular, aragonite crystals, which luminescent classically in green (marked with a small v in Figures 5 and 6), are more numerous in the cement paste generated with the biomineral particles (Figure 5), and a generally greater number of calcite crystals, which luminescent classically in orange (luminous crystals not accompanied by a small v in Figures 5 and 6), are found in the cement paste generated with the biomineral particles (Figure 6).

[0084] More generally, it should be noted that the culture solution must meet the following culture conditions: a pH between 6 and 10, under a light intensity between 1 and 2200 pmol / m². 2 / s (photosynthetic photon flux density) and a temperature between 0 and 55°C. Furthermore, the frequency of adding alkaline charge—at a given concentration—depends on the growth rate of the biomineralizing organism and the objective of maintaining a pH below 10. Example of a protocol for verifying the carbon-negative nature of the powder:

[0085] Step 1: Measurement of maximum atmospheric CO2 uptake

[0086] CO2 capture is assessed from the variation in Dissolved Inorganic Carbon (DIC, in mmol / L) of seawater, measured between two additions of alkalinity.

[0087] The reaction principle is as follows: when a source of alkalinity, whose simplified equation is Ca(OH)2 in seawater, dissolves, the alkalinity increases, which promotes the capture of atmospheric CO2 (see figure 7):

[0088] (1) Ca(OH)2 + sCO3 2 ' + (n+y)CO2^ Ca 2+ + (n+s) CO3 2 ' + H2O + yCH2O

[0089] • nCO2: quantity of atmospheric CO2 captured and mineralized

[0090] • yCO2: quantity of atmospheric CO2 captured by photosynthesis and transformed into organic matter

[0091] • sC03 2 ' : carbonate possibly already present in the alkalinity source

[0092] The calculation of CO2 capture is as follows: the amount of CO2 captured is determined by the following equation:

[0093] (2) CO2 captured (g) = ADIC (mmol / L) x Volume of seawater (L) x (44 g / mol / 1000) with:

[0094] - ADIC = final DIC - initial DIC (measured by CO2SYS from pH, AT, temperature and salinity)

[0095] - 44 g / mol: molar mass of CO2

[0096] The DIC factor can be determined by a chemical speciation calculation tool (such as CO2SYS software for example) by entering pH and Total Alkalinity (TA) data measured using a sensor or by titration, and correcting for the effect of salinity and temperature, also measured.

[0097] Step 2: Quantification of mineralized CaCO3

[0098] Mineralization by the biomineralizing organism: (3) Ca 2+ + (n+e) CO3 2 ^ (n+e) CaCO3

[0099] The mass of CaCO3 precipitated by biomineralizing organisms is determined by differential weighing after removal of organic matter.

[0100] (4) Mineral mass (g) = Total mass (g) - Organic mass (g)

[0101] Acidification method for quantifying the ratio between mineral matter and organic matter:

[0102] 1. Weigh the total mass of the sample containing the mineral phase and the organic phase

[0103] 2. Acidify the sample with 10% HCl to dissolve the CaCO3 (reaction: CaCO3 + 2H₂O) +

[0104] That 2+ + CO2| + H2O)

[0105] 3. Filter (0.2 µm) and dry the organic residue at 105°C.

[0106] 4. Weigh the stable organic mass.

[0107] Step 3: Mass balance and percentage of negative carbon

[0108] The negative carbon character of the biomineral is assessed by the ratio between the mass of CO2 mineralized in CaCO3 and the amount of CO2 captured, with two scenarios:

[0109] Case 1: 100% carbon negative: case where the mass of [CO2 captured (equation 2)] > Mass of CO2 in CaCO3 (mCaCO3 x 0.44)

[0110] Where 0.44 = mass fraction of C02 in CaC03 (44 g / mol / 100 g / mol)

[0111] Case 2: Less than 100%: Case where the exact percentage is calculated as follows:

[0112] (5) % Negative Carbon = ([mass of CO2 captured (equation 2)] / [mass of CaCO3 x 0.44]) x 100

[0113] Step 4: Verification of the "carbon negative" nature of the biomineral

[0114] Isotopic traceability is determined by measuring the δ 13 C from CaCO3 which can confirm the atmospheric origin of the mineralized carbon.

[0115] The durability of storage is determined by XRD (X-ray diffraction) analysis to confirm the crystallinity and long-term stability of the precipitated CaCO3.

[0116] Here is an experimental example of adding an alkaline source to a culture medium:

[0117] • System volume: 58 L • Temperature: 26.5 ± 1.0 °C

[0118] • Salinity: 33.5 ± 1.5 PSU

[0119] • Initial conditions: [Ca 2+ ] = 440 ppm; Alkalinity = 1.37 mmol / L (measured by titration)

[0120] Addition of alkalinity (figure 8):

[0121] • From the 16th ème Day: Addition of 0.13 meq / l / day

[0122] • From the 24th ème : addition of 0.30 meq / l / day

[0123] The following elements are observed:

[0124] • Before the addition of alkalinity: decrease in [Ca 2+ ] and alkalinity (figures 9 and 10), correlated with the growth of biomineralizing organisms (active biomineralization).

[0125] • After the 16th ème day: the addition of 0.13 meq / L / day compensates for the consumption of Ca 2+ and alkalinity by biomineralization: the concentrations stabilize (figures 9 and 10).

[0126] • After the 24th ème day: the addition of 0.30 meq / L / day exceeds consumption; [Ca 2+] and alkalinity increase, then stabilize when biomineralization adjusts to this new supply (figures 9 and 10).

[0127] Synthesis

[0128] This protocol allows for the precise quantification of atmospheric CO2 capture via the increase in DIC and for measuring the fraction of CO2 actually mineralized in the CaCO3 produced.

Claims

DEMANDS 1. A process for producing a carbon-negative biomineralized macroorganism, the process comprising the following steps: a) supplying a biomineralizing macroorganism comprising an organic phase and a mineral phase containing calcium carbonate, b) culturing, under an atmosphere comprising carbon dioxide, the biomineralizing macroorganism in a culture solution comprising salt water having a salinity of between 3 and 260 PSU and an alkalinity of between 1 mmol / L and 200 mmol / L, culture in which the biomineralizing macroorganism, during its biomineralization, produces calcium carbonate crystals, c) adding an alkaline charge to the culture solution to maintain the alkalinity of the culture solution between 1 mmol / L and 200 mmol / L and ensure the growth of the carbon-negative calcium carbonate crystals of the biomineralizing macroorganism during its biomineralization,the alkaline load being collected in the form of waste, industrial and / or mining by-products, or directly from a naturally concentrated source of alkaline elements, d) harvesting at least part of the biomineralized macroorganism when one of its average dimensions is greater than or equal to 1 cm.

2. Production method according to claim 1, wherein the biomineralizing macroorganism is selected from the group consisting of corals, macroalgae, bryozoans, or a mixture of the aforementioned macroorganisms.

3. Production method according to claim 1, wherein the macroorganism is a macroalga.

4. Production method according to claim 3, wherein the macroalga is selected from the order Bryopsidales, in particular the family Halimedaceae, and in particular the genus Halimeda.

5. Production method according to any one of claims 1 to 4, wherein, during step b) of culture, the biomineralizing macroorganism is placed on a substrate consisting of sand and / or rock fragments, or a rope.

6. Carbon-negative biomineralized macroorganism produced by implementing a process according to any one of claims 1 to 5, the biomineralized macroorganism being characterized in that it contains calcium carbonates of an aragonitic nature.

7. A method for manufacturing, at least from the biomineralized macroorganism according to claim 6, a negative carbon powder for a construction material composition, the method optionally comprising a step e) of drying the biomineralized macroorganism, followed by a step f) of first grinding the biomineralized macroorganism until ground biomineral particles are obtained, defined by a first average particle size between 5 pm and 500 pm and an organic fraction initially contained in the biomineralized macroorganism.

8. A process according to claim 7, further comprising a sieving step g1) to obtain biomineral particles separated from the organic fraction.

9. A method according to any one of claims 7 or 8, further comprising a step g2) of heating the biomineral particles to a temperature between 400°C and 600°C.

10. A method according to any one of claims 7 to 9, further comprising a step g3) of contacting the biomineral particles with a solution comprising sodium hypochlorite, sodium hydroxyl, hydrogen peroxide, or a mixture of the aforementioned elements.

11. A process according to any one of claims 7 to 10, further comprising a step h) of a second grinding until ground biomineral particles defined by a second average particle size of between 5 pm and 90 pm are obtained.

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