Sustainable building material

Abstract

A method of preparing a calcium carbonate compound comprises (i) reacting urea with an enzyme and a precipitating compound, wherein the precipitating compound comprises or consists of calcium chloride, to yield calcium carbonate and ammonium chloride; (ii) reacting the ammonium chloride to yield hydrogen chloride and ammonium hydroxide or ammonia; (iii) performing a step comprising either (iii-a1) reacting a calcium- containing mineral with the hydrogen chloride to yield the calcium chloride, wherein the calcium-containing mineral comprises calcium silicate; and when step (ii) yields ammonium hydroxide then (iii-a2) degassing the ammonium hydroxide to yield ammonia; or (iii-b1) reacting a calcium-containing mineral with the ammonium hydroxide to yield calcium hydroxide and ammonia, wherein the calcium-containing mineral comprises calcium silicate, and (iii-b2) reacting the calcium hydroxide and the hydrogen chloride to yield the calcium chloride; (iv) reacting the ammonia produced in step (ii) or step (iii) with carbon dioxide to yield an ammonium salt, wherein the ammonium salt comprises or consist of one or more of ammonium carbamate, ammonium bicarbonate and ammonium carbonate; and (v) reacting the ammonium salt to yield the urea.

Description

[0001] Sustainable Building Material

[0002] Field of the Invention

[0003] The present invention relates to a method for preparing a carbonate-based material, and in particular a carbonate-based construction material.

[0004] Background

[0005] Worldwide production of cement and concrete is responsible for around 8% of global CO2 emissions. Sustainable alternatives must be identified and scaled rapidly if we are to meet climate targets and substantially reduce greenhouse gas emissions.

[0006] While efforts to reduce the carbon footprint of concrete are limited by the inherently high production temperatures emissions from the decomposition of limestone, biologically mediated cementation offers long-term potential for decarbonizing construction.

[0007] Certain methods exist which produce bio-based materials. For example, enzyme induced carbonate precipitation (EICP) is a well-established solution used in particular for soil stabilisation, immobilisation of contaminants, and reducing soil permeability. In EICP, calcium carbonate (CaCOs) precipitation occurs via urea hydrolysis catalysed by a urease enzyme, which is typically sourced from plants. An alternative approach, as described in EP2563739A1 (Dosier) and WO2023 / 099925A1 (Sommerville et al), is Microbially Induced Calcite Precipitation (MICP), in which the urease enzyme catalysing the hydrolysis of a urea source into a carbonate precipitate is of microbial, e.g. bacterial, origin.

[0008] W02019071172A1 (Dosier et al) and US2023202859A1 (Dosier et al) disclose methods comprising a cyclic industrial process to form biocement, based on, inter alia, decomposing calcium carbonate into calcium oxide and carbon dioxide at an elevated temperature, and reacting calcium oxide with ammonium chloride to form calcium chloride, water, and ammonia gas.

[0009] There is a need for a method that allows the production of a bio-based carbonate material whilst sequestering carbon dioxide as part of a more sustainable, circular process.

[0010] It is an object of the invention to address and / or mitigate one or more problems associated with the prior art. The present invention is based on the discovery of a new methodology that allows the production of a bio-based carbonate material whilst sequestering carbon dioxide as part of a more sustainable, circular process.

[0011] According to a first aspect, there is provided a method of preparing a calcium carbonate compound, the method comprising:

[0012] (i) reacting urea with an enzyme and a precipitating compound, wherein the precipitating compound comprises or consists of calcium chloride, to yield calcium carbonate and ammonium chloride;

[0013] (ii) reacting the ammonium chloride to yield hydrogen chloride and ammonium hydroxide or ammonia;

[0014] (iii) performing a step comprising: either (iii-a1) reacting a calcium-containing mineral with the hydrogen chloride to yield the calcium chloride; and when step (ii) yields ammonium hydroxide then (iii-a2) degassing the ammonium hydroxide to yield ammonia; or

[0015] (iii-b1) reacting a calcium-containing mineral with the ammonium hydroxide to yield calcium hydroxide and ammonia, and (iii-b2) reacting the calcium hydroxide and the hydrogen chloride to yield the calcium chloride;

[0016] (iv) reacting the ammonia produced in step (ii) or step (iii) with carbon dioxide to yield an ammonium salt, wherein the ammonium salt comprises or consist of one or more of ammonium carbamate, ammonium bicarbonate and ammonium carbonate; and

[0017] (v) reacting the ammonium salt to yield the urea.

[0018] Typically, Step (i) - (v) may be carried out sequentially.

[0019] It will be appreciated, however, that, because of the circular and / or regenerative nature of the method, the method needs not start with step (i), and may be described by starting with any of steps (i)-(v).

[0020] Step (i)

[0021] Typically, the method, e.g. step (i), may comprise precipitating the calcium carbonate compound.

[0022] Step (i) may be represented by equation (1):

[0023] (NH2)2CO + CaCI2+ 2 H2O -> CaCO3+ 2 NH4CI (1) Typically, the enzyme used in step (i) may comprise a urease and / or a source thereof.

[0024] The enzyme may typically be water soluble. Step (i) may be carried out in the form of a solution or a dispersion.

[0025] The enzyme may be thermophilic or thermostable.

[0026] The enzyme may be obtainable from any plant, animal, bacterial or fungal source. The enzyme may comprise a meal of a plant, e.g. a meal of a plant of the family Leguminosae (Fabaceae), such as Jack bean meal and / or soy bean meal.

[0027] The enzyme may comprise or may consist of an enzyme obtainable from soybeans (Glycine max), jack beans (Canavalia ensiformis), watermelon seeds (Citrull us lanatus), and / or pumpkin seeds (Cucurbita pepo) or a part thereof (e.g. hulls), e.g. a meal thereof.

[0028] The method, e.g. step (i) may comprise providing the enzyme, e.g. the bean or a part thereof (e.g. hulls) or a meal thereof, in an amount or concentration in the range of 0.1 - 100 g / L, e.g. 1 - 100 g / L, typically 10-60 g / L.

[0029] The enzyme may comprise or may consist of a microbial, e.g. bacterial, enzyme, such as Proteus vulgaris, Sporosarcina ureae, Sporosarcina Pasteurii, Sporosarcina Ureae, Bacillus Sphaericus, Myxococcus Xanthus, Proteus Mirabilis, Helicobacter Pylori, Synechocystis sp. or Synechococcus sp.

[0030] The activity of the enzyme may be above 1 unit / g of the composition, e.g. of the reaction mixture, typically, in the range of about 1 to about 1 ,000,000 units, e.g. from about 10 to about 10,000units, e.g. from about 10 to about 2,500 units, e.g. from about 40 to about 400 units, per g of the composition, when measured at about 20°C

[0031] The method, e.g. step (i), may comprise adjusting the pH of the reaction mixture, e.g. below about 8, e.g. below about 7.5, e.g. between about 5 and 7.5, e.g. between about 6 and 7.5. Such pH control may help optimise reaction between the enzyme and the urea, and / or may prevent or minimise the level of ammonia degassing during step (i).

[0032] Advantageously, the enzyme may comprise or may consist of an enzyme derived from soybeans (Glycine max) or jack beans (Canavalia ensiformis). In such instance, the method, e.g. step (i) may comprise providing a soy bean source or a jack bean source, e.g. soy bean meal or jack bean meal. By such provision, a low to neutral pH may be maintained during the reaction, e.g. step (i), without the need to add an additional pH adjuster or buffer. The method may comprise milling and / or grinding beans, e.g. jack beans or soy beans, before step (i).

[0033] The method, e.g. step (i), may comprise providing a first reaction mixture comprising the urea, the enzyme and the precipitating compound.

[0034] It will be appreciated that the precipitating compound may further comprise one or more additional precipitating compound, typically a chloride salt, e.g. a chloride salt of an alkaline earth metal, e.g. magnesium chloride. In other words, in some embodiments, the precipitating compound may not consist of pure calcium chloride, but may be a mixture of calcium chloride and one or more other chloride salts.

[0035] The method, e.g. step (i), may comprise providing the first reaction mixture in a container. The container may comprise a mould. The method, e.g. step (i) may comprise preparing a moulded article.

[0036] The method, e.g. step (i), may comprise preparing a building or construction article, e.g. a brick, block, or the like.

[0037] The method may comprise providing the first reaction mixture into the container, and reacting the first reaction mixture. Providing the first reaction mixture may be carried out by any suitable means, such as feeding, injecting, pouring, percolating, the first reaction mixture, or placing the container in the first reaction mixture, such as by immersion. Typically, the method may comprise feeding, e.g. injecting, the first reaction mixture into the container.

[0038] The method, e.g. step (i), may comprise consolidating a particulate material through precipitation of the calcium carbonate. Thus, the calcium carbonate precipitate may act as a binder to consolidate the particulate material into a building or construction article.

[0039] The particulate material may comprise an aggregate or a particulate material such as sand, a biomaterial such as biochar, ceramic, glass, metal(s), metal alloy(s), or recycled aggregates such as foamed glass or the like.

[0040] Typically, the particulate material may comprise sand or sand particles, or a biomaterial such as biochar particles.

[0041] The first reaction mixture may comprise the particulate material.

[0042] Alternatively, or additionally, the particulate material may be provided in the container, e.g. mould. By such provision, the particulate material may be subjected to any desired number of injection and precipitation cycles to reach a required level of consolidation, e.g. strength, of the building or construction article. Alternatively, the method, e.g. step (i), may comprise providing the first reaction mixture on or in a support structure. In such instance, the method may not use a container such as a mould.

[0043] Preferably, the support structure may comprise or may be a low-carbon component, e.g. gypsum plaster. By such provision, the method may comprise contacting the first reaction mixture and the support structure, so as to cause calcium carbonate precipitation on or within the support structure.

[0044] The support structure may be immersed into the first reaction mixture.

[0045] The first reaction mixture may be percolated onto the support structure.

[0046] The method may comprise reiterating step (i) multiple times, e.g. at least 3, e.g. at least 6, e.g. at least 9, e.g. at least 15, e.g. at least 20 times. By such provision, each cycle of injection of the first reaction mixture and precipitation of the calcium carbonate.

[0047] The method, e.g. step (i), may comprise:

[0048] (i-a) injecting a first reaction mixture comprising urea, the enzyme and the precipitating compound into a container comprising the particulate material,

[0049] (i-b) reacting the first reaction mixture to consolidate the particulate material through precipitation of calcium carbonate;

[0050] (i-c) flushing the container of unreacted material; and

[0051] (i-d) optionally repeating steps (i-a)-(i-c).

[0052] The method, e.g. step (i) may comprise providing the urea in an amount or concentration in the range of about 0.1-4M (about 6-240 g / l), typically about 0.5-2M.

[0053] The first reaction mixture may comprise the urea in an amount or concentration in the range of about 0.1-4M (about 6-240 g / l), typically about 0.5-2M.

[0054] The method, e.g. step (i) may comprise providing the precipitating compound in an amount or concentration in the range of about 0.1-4M (about 11-444 g / l), typically about 0.5-2M.

[0055] The first reaction mixture may comprise the precipitating compound in an amount or concentration in the range of 100 - 300 g / L, e.g. 100 - 250 g / L.

[0056] Step (ii)

[0057] Advantageously, the ammonium chloride produced in step (i) may be used to perform the reaction of step (ii).

[0058] At least some of the ammonium chloride used in step (ii) may comprise the ammonium chloride produced in step (i). If required, the ammonium chloride used in step (ii) may further comprise another source of ammonium chloride. If required, the ammonium chloride solution used in step

[0059] (ii) may be concentrated via distillation and / or reverse osmosis, or may be diluted to a lower concentration with water.

[0060] Electrolysis

[0061] Step (ii) may comprise performing electrolysis on the ammonium chloride to yield hydrogen chloride and ammonium hydroxide.

[0062] Step (ii) may be represented by equation (2a):

[0063] NH4CI + H2O -> HCI + NH3.H2O (2a)

[0064] Typically, the hydrogen chloride may be in aqueous form and / or may be in the form of hydrochloric acid.

[0065] The method, e.g. step (ii), may comprise providing the ammonium chloride in an electrolyser.

[0066] The method, e.g. step (ii), may comprise providing the ammonium chloride in a cathode compartment of the electrolyser.

[0067] For example, step (ii) may be generally as described in Xie et al. (2018), the content of which is incorporated herein by reference.

[0068] In such instance, the method of preparing a calcium carbonate compound may comprise:

[0069] (i) reacting urea with an enzyme and a precipitating compound, wherein the precipitating compound comprises or consists of calcium chloride, to yield calcium carbonate and ammonium chloride;

[0070] (ii) performing electrolysis of the ammonium chloride to yield hydrogen chloride and ammonium hydroxide;

[0071] (iii) performing a step comprising: either (iii-a1) reacting a calcium-containing mineral with the hydrogen chloride produced in step (ii) to yield the calcium chloride; and (iii-a2) degassing the ammonium hydroxide produced in step (ii) to yield ammonia; or

[0072] (iii-b1) reacting a calcium-containing mineral with the ammonium hydroxide produced in step (ii) to yield calcium hydroxide and ammonia, and (iii-b2) reacting the calcium hydroxide and the hydrogen chloride produced in step (ii) to yield the calcium chloride;

[0073] (iv) reacting the ammonia produced in step (iii) with carbon dioxide to yield an ammonium salt, wherein the ammonium salt comprises or consist of one or more of ammonium carbamate, ammonium bicarbonate and ammonium carbonate; and

[0074] (v) reacting the ammonium salt to yield the urea.

[0075] Sublimation

[0076] Step (ii) may comprise sublimation of the ammonium chloride to yield hydrogen chloride and ammonia.

[0077] The method, e.g. step (ii), may comprise providing the ammonium chloride in a vessel, and heating.

[0078] Step (ii) may be represented by equation (2b):

[0079] NH4CI -> HCI (g) + NH3(g) (2b)

[0080] In such instance, the method of preparing a calcium carbonate compound may comprise:

[0081] (i) reacting urea with an enzyme and a precipitating compound, wherein the precipitating compound comprises or consists of calcium chloride, to yield calcium carbonate and ammonium chloride;

[0082] (ii) reacting the ammonium chloride to yield hydrogen chloride and ammonia;

[0083] (iii) reacting a calcium-containing mineral with the hydrogen chloride produced in step (ii) to yield the calcium chloride;

[0084] (iv) reacting the ammonia produced in step (ii) with carbon dioxide to yield an ammonium salt, wherein the ammonium salt comprises or consist of one or more of ammonium carbamate, ammonium bicarbonate and ammonium carbonate; and

[0085] (v) reacting the ammonium salt to yield the urea.

[0086] Step (iii)

[0087] Acid Route

[0088] Step (iii) may comprise step (iii-a1): reacting a calcium-containing mineral with the hydrogen chloride produced in step (ii), to yield the calcium chloride.

[0089] The calcium-containing mineral may comprise or may consist of calcium silicate and / or calcium carbonate.

[0090] Step (iii) may comprise step (iii-a1): reacting a calcium-containing mineral with the hydrogen chloride produced in step (ii), to yield the calcium chloride. At least some of the hydrogen chloride used in step (iii-a1) may comprise the hydrogen chloride produced in step (ii).

[0091] Advantageously, the calcium chloride produced in step (iii-a1) may be used as the precipitating compound in step (i).

[0092] At least some of the precipitating compound used in step (i) may comprise the calcium chloride produced in step (iii-a1).

[0093] The calcium-containing mineral may comprise or may consist of a calcium silicate material, e.g. calcium silicate.

[0094] In such instance, step (iii-a1) may comprise reacting calcium silicate with the hydrogen chloride to yield the calcium chloride and silica.

[0095] Step (iii-a1) may be represented by equation (3a1):

[0096] CaSiO3+ 2 HCI -> CaCI2+ H2O + SiO2(3a1)

[0097] The calcium-containing mineral may consist of a calcium silicate material, e.g. calcium silicate.

[0098] The calcium-containing mineral may comprise a calcium silicate material, e.g. calcium silicate, and, depending on the source of the calcium silicate material, may optionally further comprise one or more additional compounds such as magnesium silicate, fly ash, slag, recycled concrete aggregate, or basalt.

[0099] The calcium-containing mineral may be free or substantially free of calcium carbonate.

[0100] The calcium-containing mineral may comprise or may consist of a calcium carbonate material, e.g. calcium carbonate.

[0101] In such instance, step (iii-a1) may comprise reacting calcium carbonate with the hydrogen chloride to yield the calcium chloride and carbon dioxide.

[0102] Step (iii-a1) may be represented by equation (3c):

[0103] CaCO3+ 2 HCI -> CaCI2+ H2O + CO2(3c)

[0104] In such instance, the carbon dioxide generated in step (iii-a1) may be used as the carbon dioxide reacted in step (iv).

[0105] Step (iii) may further comprise step (iii-a2) degassing the ammonium hydroxide produced in step (ii), to yield ammonia. In such instance, step (iii-a2) may be represented by equation (3a2):

[0106] NH3.H2O -> NH3+ H2O (3a2) Advantageously, the ammonia produced in step (3a2) may be used as the ammonia reacted in step (iv).

[0107] At least some of the ammonia reacted in step (iv) may comprise the ammonia produced in step (iii-a2).

[0108] Thus, in an embodiment, the method may comprise:

[0109] (i) reacting urea with an enzyme and a precipitating compound, wherein the precipitating compound comprises or consists of calcium chloride, to yield calcium carbonate and ammonium chloride;

[0110] (ii) reacting the ammonium chloride to yield hydrogen chloride and ammonium hydroxide or ammonia;

[0111] (iii) performing a third step comprising:

[0112] (iii-a1) reacting a calcium silicate material with the hydrogen chloride produced in step (ii) to yield the calcium chloride and silica; and when step (ii) yields ammonium hydroxide (iii-a2) degassing the ammonium hydroxide to yield ammonia;

[0113] (iv) reacting the ammonia produced in step (ii) or step (iii) with carbon dioxide to yield an ammonium salt, wherein the ammonium salt comprises or consist of one or more of ammonium carbamate, ammonium bicarbonate and ammonium carbonate; and

[0114] (v) reacting the ammonium salt to yield the urea.

[0115] Alkali Route

[0116] Step (iii) may comprise step (iii-b1): reacting a calcium-containing mineral, e.g. a calcium silicate material, with the ammonium hydroxide produced in step (ii), to yield calcium hydroxide, silica and ammonia.

[0117] In such instance, step (iii-b1) may be represented by equation (3b1):

[0118] CaSiO3+ 2(NH3.H2O) -> Ca2++ 20FT + SiO2+ 2NH3(3b1)

[0119] At least some of the ammonium hydroxide used in step (iii-b1) may comprise the ammonium hydroxide produced in step (ii).

[0120] Advantageously, the ammonia produced in step (iii-b1) may be used as the ammonia reacted in step (iv).

[0121] Step (iii) may further comprise step (iii-b2): reacting the calcium hydroxide produced in step (iii-b1) and the hydrogen chloride produced in step (ii) to yield the calcium chloride.

[0122] In such instance, step (iii-b2) may be represented by equation (3b2): Ca2++ 2OH- + 2HCI -> CaCI2+ 2H2O (3b2)

[0123] Advantageously, the calcium chloride produced in step (iii-b2) may be used as the precipitating compound in step (i).

[0124] At least some of the precipitating compound used in step (i) may comprise the calcium chloride produced in step (iii-b2).

[0125] Thus, in an embodiment, the method may comprise:

[0126] (i) reacting urea with an enzyme and a precipitating compound, wherein the precipitating compound comprises or consists of calcium chloride, to yield calcium carbonate and ammonium chloride;

[0127] (ii) reacting the ammonium chloride to yield hydrogen chloride and ammonium hydroxide;

[0128] (iii) performing a step comprising (iii-b1) reacting a calcium silicate material with the ammonium hydroxide produced in step (ii) to yield calcium hydroxide and ammonia, and (iii-b2) reacting the calcium hydroxide and the hydrogen chloride produced in step (ii) to yield the calcium chloride;

[0129] (iv) reacting the ammonia produced in step (iii) with carbon dioxide to yield an ammonium salt, wherein the ammonium salt comprises or consist of one or more of ammonium carbamate, ammonium bicarbonate and ammonium carbonate; and

[0130] (v) reacting the ammonium salt to yield the urea.

[0131] It will be appreciated that the selection of route for step (iii), i.e. , between an “acid” route following steps (iii-a1) and (iii-a2), or an “alkaline” route following steps (iii-b1) and (iii-b2), may depend on a number of parameters, including the type of calcium-containing mineral, e.g. the type of calcium silicate material. Without wishing to be bound by theory, it is believed that an acid route may be most suitable for either calcium carbonate, or for relatively pure calcium silicate minerals (e.g., wollastonite and pseudowollastonite) and industrial waste streams rich in calcium oxide, since it minimizes processing steps. However, for more complex calcium silicate-bearing rocks (e.g., basalt) that contain other divalent cations (e.g., iron, aluminium, sodium, magnesium), an alkaline route, optionally combined with temperature control, may be more suitable as it may selectively extract calcium while leaving the other undesirable elements intact, for example as described in Gudbrandsson et al. , Geochimica et Cosmochimica Acta, 75(19), 2011 , the content of which is incorporated herein by reference. Step (iv)

[0132] Advantageously, the ammonia produced in either step (ii) or in step (iii-a2) or step (iii-b1) may be used as the ammonia reacted in step (iv). At least some of the ammonia reacted in step (iv) may comprise the ammonia produced in step (ii), step (iii-a2) or step (iii-b1).

[0133] In such instance, step (iv) may comprise one of steps (iv-a), (iv-b) or (iv-c), which may each respectively be represented by equation (4a), (4b) or (4c):

[0134] 2 N H3+ CO2-> N H2CO2N H4(4a)

[0135] NH3+ CO2+ H2O -> NH4HCO3(4b)

[0136] 2 NH3+ CO2+ H2O -> (NH4)2CO3(4C)

[0137] Step (iv-a) may yield ammonium carbamate.

[0138] Step (iv-b) may yield ammonium bicarbonate.

[0139] Step (iv-c) may yield ammonium carbonate.

[0140] It will be appreciated that the particular ammonium salt produced in step (iv) may depend on the reaction conditions between the ammonia and the carbon dioxide. For example, anhydrous conditions may be preferred to favour the formation of carbamate (NH3CC>2) and / or to avoid the competitive formation of HCO3and CO3through the complex series of equilibrium reactions 1-5:

[0141] 1) NH3+CO2+H2O NH4++ HCO3-

[0142] A typical anhydrous setup involves feeding gaseous NH3and CO2 through an organic solvent such as ethanol, 1-propanol, or DMF. The NH3to CO2 ratio and gas flow rate dictate the CO2 capture rate and NH3conversion efficiency. Barzagli et al. (2011) found that an NH3 / CC>2 molar ratio of 1.5 is optimal for CO2 capture (85-90%) and NH3utilization (94-98%). The selective formation of ammonium carbamate is preferred because it can be efficiently converted directly to urea through a dehydration reaction. The conversion of ammonium bicarbonate to urea is less efficient and limited to 50% due to the constraints of reaction 6: 6) 2NH4HCO3' -> (NH2)2CO + CO2+ 3H2O

[0143] Achieving anhydrous conditions may not always be practical due to factors such as the hygroscopic nature of NH3, the presence of moisture in industrial environments, and the challenges associated with completely removing water from the system. In this case unconverted ammonium bicarbonate and reaction by-products (e.g. CO2, H2O, NH3) following dehydration can be recovered and recycled for further processing.

[0144] In keeping with this, alternatively the ammonium hydroxide solution produced in step (ii) may be used directly as a scrubber for CO2gas (Hamouda, Eldien & Abadir. 2020). Due to the high water content, the resulting salt is primarily ammonium bicarbonate. This approach may have more practical applications, but requires additional dehydration steps due to the stoichiometry of reaction (6).

[0145] The method, e.g. step (iv), may comprise bubbling the ammonia and the carbon dioxide in a liquid, e.g. in an aqueous solution. The aqueous solution may comprise a mixture of water and an organic solvent such as an alcohol, e.g. water and ethanol. Step (iv) may be substantially as described for example in Barzagli et al, 2011 and / or Barzagli et al. 2016, the contents of which are incorporated herein by reference.

[0146] Step (v)

[0147] Advantageously, the ammonium salt produced in step (iv) may be used to prepare the urea used in step (i).

[0148] At least some of the ammonium salt used in step (iv) may comprise the ammonium salt produced in step (iv).

[0149] Thus, step (v) may comprise one of steps (v-a), (v-b) or (v-c), which may each respectively be represented by equation (5a), (5b) or (5c):

[0150] N H2CO2N H4-> (N H2)2CO + H2O (5a)

[0151] 2 NH4HCO3-> (NH2)2CO + 3 H2O + CO2(5b)

[0152] (NH4)2CO3-> (NH2)2CO + 2 H2O (5C)

[0153] Step (v) may be substantially as described for example in Barzagli et al. 2016, the content of which is incorporated herein by reference The method, e.g. step (v), may comprise heating the ammonium salt, e.g. in a sealed container.

[0154] The method, e.g. step (v), may comprise heating the ammonium salt to about 150°C to 180°C, e.g. about 155°C to 170°C, e.g. about 165°C, for at least 30 minutes, e.g. at least 60 mins, e.g. about 90 mins.

[0155] According to a second aspect, there is provided a method of preparing a calcium carbonate compound, the method comprising:

[0156] (i) reacting urea with an enzyme and a precipitating compound, wherein the precipitating compound comprises or consists of calcium chloride, to yield calcium carbonate and ammonium chloride;

[0157] (ii) reacting the ammonium chloride to yield hydrogen chloride and ammonium hydroxide or ammonia;

[0158] (iii) performing a third step comprising:

[0159] (iii-a1) reacting a calcium silicate material with the hydrogen chloride produced in step (ii) to yield the calcium chloride and silica; and when step (ii) yields ammonium hydroxide then (iii-a2) degassing the ammonium hydroxide to yield ammonia;

[0160] (iv) reacting the ammonia produced in step (ii) or step (iii) with carbon dioxide to yield an ammonium salt, wherein the ammonium salt comprises or consist of one or more of ammonium carbamate, ammonium bicarbonate and ammonium carbonate; and

[0161] (v) reacting the ammonium salt to yield the urea.

[0162] According to a third aspect, there is provided a method of preparing a calcium carbonate compound, the method comprising:

[0163] (i) reacting urea with an enzyme and a precipitating compound, wherein the precipitating compound comprises or consists of calcium chloride, to yield calcium carbonate and ammonium chloride;

[0164] (ii) reacting the ammonium chloride to yield hydrogen chloride and ammonium hydroxide or ammonia;

[0165] (iii) performing a third step comprising (iii-a1) reacting a calcium carbonate material with the hydrogen chloride produced in step (ii) to yield the calcium chloride and carbon dioxide; and when step (ii) yields ammonium hydroxide then (iii-a2) degassing the ammonium hydroxide to yield ammonia; (iv) reacting the ammonia produced in step (ii) or step (iii) with the carbon dioxide produced in step (iii) to yield an ammonium salt, wherein the ammonium salt comprises or consist of one or more of ammonium carbamate, ammonium bicarbonate and ammonium carbonate; and

[0166] (v) reacting the ammonium salt to yield the urea.

[0167] According to a fourth aspect, there is provided a method of preparing a calcium carbonate compound, the method comprising:

[0168] (i) reacting urea with an enzyme and a precipitating compound, wherein the precipitating compound comprises or consists of calcium chloride, to yield calcium carbonate and ammonium chloride;

[0169] (ii) reacting the ammonium chloride to yield hydrogen chloride and ammonium hydroxide;

[0170] (iii) performing a step comprising (iii-b1) reacting a calcium silicate material with the ammonium hydroxide produced in step (ii) to yield calcium hydroxide and ammonia, and (iii-b2) reacting the calcium hydroxide and the hydrogen chloride produced in step (ii) to yield the calcium chloride;

[0171] (iv) reacting the ammonia produced in step (iii) with carbon dioxide to yield an ammonium salt, wherein the ammonium salt comprises or consist of one or more of ammonium carbamate, ammonium bicarbonate and ammonium carbonate; and

[0172] (v) reacting the ammonium salt to yield the urea.

[0173] According to a fifth aspect, there is provided a method of preparing a calcium carbonate compound, the method comprising:

[0174] (i) reacting urea with an enzyme and a precipitating compound, wherein the precipitating compound comprises or consists of calcium chloride, to yield calcium carbonate and ammonium chloride;

[0175] (ii) performing a step comprising:

[0176] (ii-a1) reacting the ammonium chloride with sodium hydroxide to yield sodium chloride and ammonia; and

[0177] (ii-a2) reacting the sodium chloride to yield hydrogen chloride and the sodium hydroxide;

[0178] (iii) reacting a calcium-containing mineral with the hydrogen chloride produced in step (ii-a2) to yield the calcium chloride; (iv) reacting the ammonia produced in step (ii-a1) with carbon dioxide to yield an ammonium salt, wherein the ammonium salt comprises or consist of one or more of ammonium carbamate, ammonium bicarbonate and ammonium carbonate; and

[0179] (v) reacting the ammonium salt to yield the urea.

[0180] Typically, Step (i) - (v) may be carried out sequentially.

[0181] It will be appreciated, however, that, because of the circular and / or regenerative nature of the method, the method needs not start with step (i), and may be described by starting with any of steps (i)-(v).

[0182] Step (i)

[0183] Step (i) may be as described above in relation to the first aspect.

[0184] Step (ii)

[0185] In this embodiment, step (ii) may comprise two sub-steps.

[0186] Alkaline stripping of ammonia

[0187] In a first sub-step (ii-a1), the method may comprise reacting the ammonium chloride with sodium hydroxide to yield sodium chloride and ammonia.

[0188] Advantageously, this allows direct recovery of gaseous ammonia, which may help eliminate NH3crossover and / or hydrogen co-migration issues associated with NH4CI electrolysis, thereby improving overall nitrogen recovery and / or carbon efficiency. This may also allow for a more modular architecture, with NH3recovery handled chemically rather than electrochemically.

[0189] Advantageously, the ammonia produced in step (ii-a1) may be used as feed in step (iv).

[0190] Electrolysis

[0191] In a second sub-step (ii-a2) the method may comprise performing electrolysis on the sodium chloride to yield hydrogen chloride and the sodium hydroxide. Advantageously, the sodium hydroxide is regenerated in step (ii-a2) and may be reused in step (ii-a1).

[0192] Step (ii-a1) may be represented by equation (2a2):

[0193] 2NaCI + H2O -> 2HCI + 2NaOH (2a2) Typically, the hydrogen chloride may be in aqueous form and / or may be in the form of hydrochloric acid.

[0194] The method, e.g. step (ii-a1), may comprise providing the sodium chloride in an electrolyser.

[0195] The method, e.g. step (ii-a1), may comprise providing the sodium chloride in a cathode compartment of the electrolyser.

[0196] Thus, the method of preparing a calcium carbonate compound may comprise:

[0197] (i) reacting urea with an enzyme and a precipitating compound, wherein the precipitating compound comprises or consists of calcium chloride, to yield calcium carbonate and ammonium chloride;

[0198] (ii) performing a step comprising:

[0199] (ii-a1) reacting the ammonium chloride with sodium hydroxide to yield sodium chloride and ammonia; and

[0200] (ii-a2) performing electrolysis on the sodium chloride to yield hydrogen chloride and the sodium hydroxide;

[0201] (iii) reacting a calcium-containing mineral with the hydrogen chloride produced in step (ii-a2) to yield the calcium chloride;

[0202] (iv) reacting the ammonia produced in step (ii-a1) with carbon dioxide to yield an ammonium salt, wherein the ammonium salt comprises or consist of one or more of ammonium carbamate, ammonium bicarbonate and ammonium carbonate; and

[0203] (v) reacting the ammonium salt to yield the urea.

[0204] It will be appreciated that step (ii-a2) may yield hydrogen chloride directly or indirectly.

[0205] Step (ii-a2) may yield hydrogen chloride directly. In such instance, step (ii-a2) may comprise reacting the sodium chloride, e.g. performing electrolysis on sodium chloride, to yield hydrogen chloride, e.g. in aqueous form, and the sodium hydroxide.

[0206] Step (ii-a2) may yield hydrogen chloride indirectly. In such instance, step (ii-a2) may comprise reacting the sodium chloride, e.g. performing electrolysis on sodium chloride, to yield hydrogen gas (H2) and chlorine gas (Cl2), and the sodium hydroxide. In such instance, hydrogen gas (H2) and chlorine gas (Cl2) may be subsequently combined, e.g. in an aqueous solution, to produce the hydrogen chloride. the electrolysis of NaCI solution to produce H2and Cl2, which could later be combined to produce HCI. While this route is more energy-intensive, it would allow us to integrate with the existing chlor-alkali process. Importantly, the mass balance does not change.

[0207] Advantageously, this approach allows improved water and salt management, as NaCI is easier to concentrate via reverse osmosis.

[0208] Step (iii)

[0209] Step (iii) may comprise reacting a calcium-containing mineral with the hydrogen chloride produced in step (ii-a2) to yield the calcium chloride.

[0210] The calcium-containing mineral may comprise or may consist of calcium silicate and / or calcium carbonate.

[0211] At least some of the hydrogen chloride used in step (iii) may comprise the hydrogen chloride produced in step (ii-a2).

[0212] Advantageously, the calcium chloride produced in step (iii) may be used as the precipitating compound in step (i).

[0213] At least some of the precipitating compound used in step (i) may comprise the calcium chloride produced in step (iii).

[0214] The calcium-containing mineral may comprise or may consist of a calcium silicate material, e.g. calcium silicate.

[0215] In such instance, step (iii) may comprise reacting calcium silicate with the hydrogen chloride to yield the calcium chloride and silica.

[0216] Step (iii) may be represented by equation (3a1):

[0217] CaSiO3+ 2HCI -> CaCI2+ H2O + SiO2(3a1)

[0218] The calcium-containing mineral may consist of a calcium silicate material, e.g. calcium silicate.

[0219] The calcium-containing mineral may comprise a calcium silicate material, e.g. calcium silicate, and, depending on the source of the calcium silicate material, may optionally further comprise one or more additional compounds such as magnesium silicate, fly ash, slag, recycled concrete aggregate, or basalt.

[0220] The calcium-containing mineral may be free or substantially free of calcium carbonate.

[0221] The calcium-containing mineral may comprise or may consist of a calcium carbonate material, e.g. calcium carbonate. In such instance, step (iii-a1) may comprise reacting calcium carbonate with the hydrogen chloride to yield the calcium chloride and carbon dioxide.

[0222] Step (iii-a1) may be represented by equation (3c):

[0223] CaCO3+ 2HCI -> CaCI2+ H2O + CO2(3c)

[0224] In such instance, the carbon dioxide generated in step (iii) may be used as the carbon dioxide reacted in step (iv).

[0225] Step (iv)

[0226] Step (iv) may be as described above in relation to the first aspect, except that the ammonia is obtained from step (ii-a1).

[0227] Step (v)

[0228] Step (v) may be as described above in relation to the first aspect.

[0229] According to a sixth aspect, there is provided a calcium carbonate compound, e.g. a building or construction material, obtainable or obtained according to a method according to any of the first to fifth aspects.

[0230] The features described in relation to any aspect of the invention may equally apply to any other aspect and, merely for brevity, are not repeated. For example, features described in relation to compositions can apply in relation to methods, and vice versa.

[0231] Brief Description of Drawings

[0232] Embodiments of the invention are described with reference to the accompanying drawings, in which:

[0233] Figure 1 shows a method of preparing a calcium carbonate compound, according to a first embodiment;

[0234] Figure 2 shows a method of preparing a calcium carbonate compound, according to a second embodiment;

[0235] Figure 3 shows a method of preparing a calcium carbonate compound, according to a third embodiment;

[0236] Figure 4a shows a perspective view of a mould for preparing a construction article, according to an embodiment; Figure 4b shows a cross-sectional view of the mould of Figure 4a, before injection of a reaction mixture;

[0237] Figure 4c shows a cross-sectional view of the mould of Figure 4a, following reaction;

[0238] Figure 5 illustrates a construction article made according to the present method after (a) 3, (b) 6, and (c) 9 bio-precipitation cycles;

[0239] Figure 6 shows a construction article made according to the present method according to another embodiment;

[0240] Figures 7a and 7b show X-ray computed tomography (XCT) images of an article according to an embodiment, before (Fig 7a) and after (Fig 7b) precipitation;

[0241] Figure 7c show an X-ray computed tomography (XCT) image of the article of Figure 7b, with calcite highlighted in colour;

[0242] Figure 8 shows a method of preparing a calcium carbonate compound, according to a fourth embodiment.

[0243] Detailed Description

[0244] In the present disclosure, reference is made to a number of terms, which have the meanings provided below, unless a context indicates to the contrary. The nomenclature used herein for defining compounds, in particular the compounds according to the invention, is in general based on the rules of the IIIPAC organisation for chemical compounds, specifically the “IIIPAC Compendium of Chemical Terminology (Gold Book)”. For the avoidance of doubt, if a rule of the IIIPAC organisation is in conflict with a definition provided herein, the definition herein is to prevail. Furthermore, if a compound structure is in conflict with the name provided for the structure, the structure is to prevail.

[0245] The term “comprising” or variants thereof is to be understood herein to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

[0246] The term “consisting” or variants thereof is to be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, and the exclusion of any other element, integer or step or group of elements, integers or steps.

[0247] The term “about” herein, when qualifying a number or value, is used to refer to values that lie within ± 5% of the value specified. For example, if a temperature is specified to be about 5 to about 13 °C, temperatures of 4.75 to 13.65 °C are included. Reference to physical states of matter (such as liquid or solid) refer to the matter’s state at 25 °C and atmospheric pressure unless the context dictates otherwise.

[0248] As explained above, the present inventors have discovered that it is possible to

[0249] Figure 1 shows a method 100 of preparing a calcium carbonate compound, according to a first embodiment.

[0250] In this embodiment, the method may be referred to as an “acid” route, due to the calcium silicate compound used in step 130 being reacted with HCI.

[0251] Advantageously, the method 100 is a generally circular method. Therefore, the terms “first”, “second” “third”, “fourth” or “fifth” will not herein be understood as necessarily starting with a “first” step and ending with a “fifth” step, but are merely used to identify these steps relative to each other and describe each of them individually.

[0252] Step 110

[0253] The first step 110 comprises precipitating a calcium carbonate compound.

[0254] Step 110 may be represented by equation (1):

[0255] (NH2)2CO + CaCI2+ 2 H2O -> CaCO3+ 2 NH4CI (1)

[0256] Typically, step 110 requires the use of a urease enzyme, which is typically water soluble. Step (i) is typically carried out in the form of a solution or a dispersion.

[0257] The enzyme may be obtainable from any plant, animal, bacterial or fungal source. In this embodiment, the enzyme is obtained from soybeans (Glycine max) and / or jack beans (Canavalia ensiformis).

[0258] The method, e.g. step (i) may comprise providing the enzyme, e.g. the bean or meal thereof, in an amount or concentration in the range of 0.1 - 100 g / L, e.g. 1 - 100 g / L, typically 10-60 g / L.

[0259] The activity of the enzyme may be above 1 unit / g of the composition, e.g. of the reaction mixture, typically, in the range of about 1 to about 1 ,000,000 units, e.g. from about 10 to about 10,000units, e.g. from about 10 to about 2,500 units, e.g. from about 40 to about 400 units, per g of the composition, when measured at about 20°C.

[0260] Typically, 0.1-100 g / l bean, is ground to a fine powder (<300 pm) before being mixed with water (e.g. de-ionized, purified, tap or saltwater). A coagulant (e.g. calcium sulphate, calcium chloride or magnesium chloride) may be added, typically at <10 g / l, to remove unwanted bean mass prior to filtration.

[0261] Advantageously, because the enzyme comprises or consists of an enzyme derived from soybeans (Glycine max) or jack beans (Canavalia ensiformis), a low to neutral pH may be maintained during the reaction (1), without the need to add an additional pH adjuster or buffer. This may advantageously reduce the risk of ammonia degassing and may help maintain ammonium chloride in solution.

[0262] Typically, in step 110, urea is provided in the reaction mixture in an amount or concentration in the range of about 0.1-4M (about 6-240 g / l), typically about 0.5-2M.

[0263] Typically, in step 110, the precipitating compound in the form of calcium chloride is provided in the reaction mixture in an amount or concentration in the range of about 0.1-4M (about 11-444 g / l), typically about 0.5-2M.

[0264] Step 120

[0265] As shown in Figure 1 , the ammonium chloride produced in step 110 is used to perform the hydrolysis of step 120.

[0266] Thus, in this embodiment, step (ii) comprises reacting the ammonium chloride to yield hydrogen chloride and ammonium hydroxide. However, it will be appreciated that, as explained above, alternative options for decomposing the ammonium chloride may be used, such as sublimating the ammonium chloride into hydrogen chloride and ammonia. In such instance, the ammonia gas produced in step (ii) may be used as the ammonia reacted in step (iv).

[0267] In this embodiment based on an electrolysis step, at least some of the ammonium chloride used in the hydrolysis of step 120 comprises the ammonium chloride produced in step 120. If more ammonium chloride is required due to inevitable losses during the method 100, then a small amount of additional ammonium chloride may be supplied in step 120.

[0268] Step 120 may be represented by equation (2):

[0269] NH4CI + H2O -> HCI + NH3.H2O (2)

[0270] Typically, the hydrogen chloride is in aqueous form and / or is in the form of hydrochloric acid.

[0271] Step 120 comprises providing the ammonium chloride in an electrolyser.

[0272] The method, e.g. step (ii), may comprise providing the ammonium chloride in a cathode compartment of the electrolyser.

[0273] Step 130

[0274] Step 130 generally describes a step of reacting a calcium-containing mineral with one of the compounds generated in step 120, in order to yield calcium chloride. In the embodiment of Figure 1 , the calcium-containing mineral used in step 130 is a calcium silicate material. However, alternatively, calcium carbonate may be used, as described below in relation to the embodiment of Figure 3.

[0275] Although, for the purpose of Figure 1 and Figure 2, the calcium-containing mineral is shown as calcium silicate, it will be appreciated that, depending on the source of the calcium silicate material, calcium silicate mineral may optionally further comprise one or more additional compounds such as magnesium silicate, fly ash, slag, recycled concrete aggregate, or basalt.

[0276] In the embodiment of Figure 1 , step 130 represents an “acid” route, due to the calcium silicate compound used in step 130 being reacted with HCI generated in step 120. An alternative “alkali” route is described in relation to Figure 2.

[0277] Step 130 includes a first step 131 comprising reacting a calcium silicate material with the hydrogen chloride produced in step 120, to yield the calcium chloride and silica.

[0278] At least some of the hydrogen chloride used in step 131 comprises the hydrogen chloride produced in step 120. If more hydrogen chloride is required due to inevitable losses during the method 100, then a small amount of additional hydrogen chloride may be supplied in step 131.

[0279] Step 131 may be represented by equation (3a1):

[0280] CaSiO3+ 2 HCI -> CaCI2+ H2O + SiO2(3a1)

[0281] Advantageously, the calcium chloride produced in step 131 is used as the precipitating compound in step 110.

[0282] At least some of the precipitating compound used in step 110 comprises the calcium chloride produced in step 131. If more calcium chloride is required due to inevitable losses during the method 100, then a small amount of additional calcium chloride may be supplied in step 110. It will be appreciated that the precipitating compound may further comprise one or more additional precipitating compound, typically a chloride salt, e.g. a chloride salt of an alkaline earth metal, e.g. magnesium chloride. In other words, the precipitating compound may not be pure calcium chloride, but may be a mixture of calcium chloride and one or more other chloride salts.

[0283] Step 130 further comprises step 132 comprising degassing the ammonium hydroxide produced in step 120, to yield ammonia. In such instance, 132 can be represented by equation (3a2):

[0284] NH3.H2O -> NH3+ H2O (3a2) Advantageously, the ammonia produced in step 132 can be used as the ammonia reacted in step 140.

[0285] At least some of the ammonia reacted in step 140 comprises the ammonia produced in step 132. If more ammonia is required due to inevitable losses during the method 100, then a small amount of ammonia may be supplied in step 140.

[0286] It will be appreciated that the selection of route for the calcium silicate reaction, i.e., between an “acid” route following step 130 of Figure 1 and Figure 3 or an “alkaline” route following step 230 of Figure 2, may depend on a number of parameters, including the type of calcium-containing mineral. Without wishing to be bound by theory, it is believed that an acid route may be most suitable for either calcium carbonate or for relatively pure calcium silicate minerals (e.g., wollastonite and pseudowollastonite) and industrial waste streams rich in calcium oxide, since it minimizes processing steps. However, for more complex calcium silicate-bearing rocks (e.g., basalt) that contain other divalent cations (e.g., iron, aluminium, sodium, magnesium), an alkaline route, optionally combined with temperature control, may be more suitable as it may selectively extract calcium while leaving the other undesirable elements intact, for example as described in Gudbrandsson et al. , Geochimica et Cosmochimica Acta, 75(19), 2011 , the content of which is incorporated herein by reference.

[0287] Step 140

[0288] Step 140 generally describes reacting the ammonia produced in step 132, to produce an ammonium salt.

[0289] At least some of the ammonia reacted in step 140 comprises the ammonia produced in step 132. If more ammonia is required due to inevitable losses during the method 100, then a small amount of ammonia may be supplied in step 140.

[0290] Step 140 may comprise one of steps 140a, 140b or 140c, which may each respectively be represented by equation (4a), (4b) or (4c):

[0291] 2 N H3+ CO2-> N H2CO2N H4(4a)

[0292] NH3+ CO2+ H2O -> NH4HCO3(4b)

[0293] 2 NH3+ CO2+ H2O -> (NH4)2CO3(4C)

[0294] Step 140a yields ammonium carbamate.

[0295] Step 140b yields ammonium bicarbonate.

[0296] Step 140c yields ammonium carbonate. It will be appreciated that the particular ammonium salt produced in step 140 may depend on the reaction conditions between the ammonia and the carbon dioxide. For example, anhydrous conditions are preferred to favour the formation of carbamate (NH3CO2) and / or to avoid the competitive formation of HCO3 and CO3 through the complex series of equilibrium reactions 1-5:

[0297] 1) NH3+CO2+H2O NH4++ HCOs'

[0298] A typical anhydrous setup involves feeding gaseous NH3 and CO2 through an organic solvent such as ethanol, 1-propanol, or DMF. The NH3 to CO2 ratio and gas flow rate dictate the CO2 capture rate and NH3 conversion efficiency. Barzagli et al. (2011) found that an NH3 / CO2 molar ratio of 1 .5 is optimal for CO2 capture (85-90%) and NH3 utilization (94-98%). The selective formation of ammonium carbamate is preferred because it can be efficiently converted directly to urea through a dehydration reaction. The conversion of ammonium bicarbonate to urea is less efficient and limited to 50% due to the constraints of reaction 6:

[0299] 6) 2NH4HCO3- -> (NH2)2CO + CO2+ 3H2O

[0300] Achieving anhydrous conditions may not always be practical due to factors such as the hygroscopic nature of NH3, the presence of moisture in industrial environments, and the challenges associated with completely removing water from the system. In this case unconverted ammonium bicarbonate and reaction by-products (e.g. CO2, H2O, NH3) following dehydration can be recovered and recycled for further processing.

[0301] In keeping with this, alternatively the ammonium hydroxide solution produced in step (ii) can be used directly as a scrubber for CO2 gas (Hamouda, Eldien & Abadir. 2020). Due to the high water content, the resulting salt is primarily ammonium bicarbonate. This approach may have more practical applications, but requires additional dehydration steps due to the stoichiometry of reaction 6. The method, e.g. step 140, typically comprises bubbling the ammonia and the carbon dioxide in a mixture of water and ethanol. Step 140 may be substantially as described for example in Barzagli et al, 2011 and / or Barzagli et al. 2016, the contents of which are incorporated herein by reference.

[0302] Step 150

[0303] Step 150 generally describes converting the ammonium salt generated in step 140, into urea.

[0304] Thus, the ammonium salt produced in step 140 is used to prepare the urea used in step 110.

[0305] At least some of the ammonium salt used in step 150 comprises the ammonium salt produced in step 140. If more ammonium salt is required due to inevitable losses during the method 100, then a small amount of ammonium salt may be supplied in step 150.

[0306] Step 150 may comprise one of steps 150a, 150b, or 150c, which can each respectively be represented by equation (5a), (5b) or (5c), depending on the type of ammonium salt that is generated in step 140:

[0307] N H2CO2N H4-> (N H2)2CO + H2O (5a)

[0308] 2 NH4HCO3-> (NH2)2CO + 3 H2O + CO2(5b)

[0309] (NH4)2CO3-> (NH2)2CO + 2 H2O (5c)

[0310] Step 150 may be substantially as described for example in Barzagli et al. 2016, the content of which is incorporated herein by reference

[0311] The method, e.g. step 150 typically comprises heating the ammonium salt in a sealed container, in this embodiment at about 165°C for about 90 mins.

[0312] Figure 2 shows a method 200 of preparing a calcium carbonate compound, according to a second embodiment.

[0313] The method 200 of Figure 2 is generally similar to the method 100 of Figure 1 , like steps denoted by like numerals, incremented by “100”.

[0314] However, in this embodiment, the third step 230 represents an “alkali” route, due to the calcium silicate compound used in step 230 being reacted with ammonium hydroxide generated in step 220. Step 230 comprises step 231 comprising reacting a calcium silicate material with the ammonium hydroxide produced in step 220, to yield calcium hydroxide, silica and ammonia.

[0315] Step 231 may be represented by equation (3b1):

[0316] CaSiO3+ 2(NH3.H2O) -> Ca2++ 2OH’ + SiO2+ 2NH3(3b1)

[0317] At least some of the ammonium hydroxide used in step 231 may comprise the ammonium hydroxide produced in step 220. If more ammonium hydroxide is required due to inevitable losses during the method 200, then a small amount of additional ammonium hydroxide may be supplied in step 231.

[0318] Advantageously, the ammonia produced in step 231 is used as the ammonia reacted in step 240.

[0319] Step 230 further comprise step 232 comprising reacting the calcium hydroxide produced in step 231 and the hydrogen chloride produced in step 220 to yield calcium chloride.

[0320] Step 232 can be represented by equation (3b2):

[0321] Ca2++ 2OH- + 2HCI -> CaCI2+ 2H2O (3b2)

[0322] Advantageously, the calcium chloride produced in step 232 may be used as the precipitating compound in step 210. If more calcium chloride is required due to inevitable losses during the method 200, then a small amount of additional calcium chloride may be supplied in step 210.

[0323] Figure 3 shows a method 300 of preparing a calcium carbonate compound, according to a third embodiment.

[0324] The method 300 of Figure 3 is generally similar to the method 100 of Figure 1 , like steps denoted by like numerals, incremented by “100”.

[0325] Like in Figure 1 , in this embodiment, the third step 330 represents an “acid” route, due to the calcium-containing mineral used in step 330 being reacted with hydrogen chloride generated in step 320. However, in this embodiment, the calcium-containing mineral is calcium carbonate.

[0326] Thus, in this embodiment, step 330 includes a first step 331 comprising reacting a calcium carbonate material with the hydrogen chloride produced in step 320, to yield the calcium chloride and carbon dioxide.

[0327] At least some of the hydrogen chloride used in step 331 comprises the hydrogen chloride produced in step 320. If more hydrogen chloride is required due to inevitable losses during the method 300, then a small amount of additional hydrogen chloride may be supplied in step 331.

[0328] Step 331 may be represented by equation (3d):

[0329] CaCO3+ 2 HCI -> CaCI2+ H2O + CO2(3d)

[0330] Advantageously, the calcium chloride produced in step 331 is used as the precipitating compound in step 310.

[0331] At least some of the precipitating compound used in step 310 comprises the calcium chloride produced in step 331. If more calcium chloride is required due to inevitable losses during the method 300, then a small amount of additional calcium chloride may be supplied in step 310.

[0332] Also, the carbon dioxide produced in step 331 may be used as at least some of the carbon dioxide reacted in step 340. Whilst this may reduce the amount of external carbon dioxide sequestered by the present method, this approach may ensure the use of a reliable and pure source of carbon dioxide in step 340.

[0333] It will also be appreciated that a combination of sources of calcium-containing minerals may be used, such as a

[0334] Like in Figure 1 , step 330 of Figure 3 further comprises step 332 comprising degassing the ammonium hydroxide produced in step 320, to yield ammonia. In such instance, 332 can be represented by equation (3c2):

[0335] NH3.H2O -> NH3+ H2O (3C2)

[0336] Advantageously, the ammonia produced in step 332 can be used as the ammonia reacted in step 340.

[0337] At least some of the ammonia reacted in step 340 comprises the ammonia produced in step 332. If more ammonia is required due to inevitable losses during the method 300, then a small amount of ammonia may be supplied in step 340.

[0338] Figure 8 shows a method 700 of preparing a calcium carbonate compound, according to another embodiment.

[0339] The method 700 of Figure 8 is generally similar to the method 100 of Figure 1 , like steps denoted by like numerals, incremented by “600”.

[0340] However, in this embodiment, the second step 720 and the third step 730 are slightly different from steps 120 and 130 of Figure 1.

[0341] In this embodiment, second step 720 comprises two sub-steps 721 and 722. Step 721 comprises reacting the ammonium chloride generated in step 710 with sodium hydroxide to yield sodium chloride and ammonia.

[0342] Advantageously, this allows direct recovery of gaseous ammonia, which may help eliminate NH3crossover and / or hydrogen co-migration issues associated with NH4CI electrolysis, thereby improving overall nitrogen recovery and / or carbon efficiency. This may also allow for a more modular architecture, with NH3recovery handled chemically rather than electrochemically.

[0343] Advantageously, the ammonia produced in step 720 is used as feed in step (740).

[0344] Second sub-step 722 comprises performing electrolysis on the sodium chloride to yield hydrogen chloride and the sodium hydroxide, which sodium hydroxide can then be reused in step 721.

[0345] Step 730 comprises reacting a calcium silicate material with the hydrogen chloride produced in step 721 , to yield the calcium chloride and silica.

[0346] At least some of the hydrogen chloride used in step 730 comprises the hydrogen chloride produced in step 722. If more hydrogen chloride is required due to inevitable losses during the method 700, then a small amount of additional hydrogen chloride may be supplied in step 730.

[0347] Step 730 may be represented by equation (3a1):

[0348] CaSiO3+ 2 HCI -> CaCI2+ H2O + SiO2(3a1)

[0349] Advantageously, the calcium chloride produced in step 730 is used as the precipitating compound in step 710.

[0350] At least some of the precipitating compound used in step 710 comprises the calcium chloride produced in step 730. If more calcium chloride is required due to inevitable losses during the method 700, then a small amount of additional calcium chloride may be supplied in step 710. It will be appreciated that the precipitating compound may further comprise one or more additional precipitating compound, typically a chloride salt, e.g. a chloride salt of an alkaline earth metal, e.g. magnesium chloride. In other words, the precipitating compound may not be pure calcium chloride, but may be a mixture of calcium chloride and one or more other chloride salts.

[0351] Step 740 is generally similar to step 140 as described with reference to Figure 1 , except that the ammonia is obtained from step (721).

[0352] Steps 750 and 710 are generally similar to steps 150 and 110 as described with reference to Figure 1 . Figure 4a shows a perspective view of a mould 401 for preparing a construction article 470, according to an embodiment. Figure 4b shows a cross-sectional view of the mould 401 of Figure 4a, before injection of a reaction mixture, and Figure 4c shows a cross-sectional view of the mould 401 of Figure 4a, following reaction, showing the construction article 470 consolidated within the mould 401.

[0353] The mould 401 has an inlet 461 near a bottom portion of the mould 401 , used for injecting a reaction mixture into the mould. The reaction mixture may typically be as described above in step (i), and in this example includes a solution of urea, calcium chloride, and a urease enzyme such as jack bean urease or soy bean urease.

[0354] The mould includes a mould cavity 465, as best shown in Figure 4(b).

[0355] The mould 401 , e.g. the cavity 465 is provided, e.g. filled, with a particulate material, in this example sand, which is consolidated inside the mould through precipitation of calcium carbonate.

[0356] In use, the mixture is injected into the mould 401 via inlet 461 , and allowed to react to cause precipitation of calcium carbonate.

[0357] As shown in Figure 3(b), a perforated region 466 is provided at the top and bottom sides such that the mixture injected via inlet 461 passes through the perforated region 466, allowing even distribution of fluids through the aggregate.

[0358] Upon precipitation, which is herein described as an injection cycle, the injection pump (not shown) is actuated in reverse in order to withdraw any unreacted compounds within the mould cavity 465.

[0359] This process may be repeated multiple times, for example 5-10 times, in order to obtain a desired level of consolidation, e.g. a predetermined strength, in the product 470. For example, the article may have a compressive strength of at least 3 N / mm2, e.g. at least 10 N / mm2(as measured following ASTM C39) and / or a thermal conductivity of less than 5 W / m K, e.g. less than 2 W / m K, e.g. less than 1 W / m K, e.g. less than 0.5 W / m K, e.g. about 0.3 - 1 W / m K.

[0360] Advantageously, the mould 401 may be rotated 180°, such that outlet 462 will become the inlet and the inlet 461 will become the outlet, in order to improve the homogeneity of the resulting article 470.

[0361] Alternatively, or additionally, the mould 401 may be rotated onto other sides, for examples when a gravity-dominated precipitation mechanism is used, e.g. when the reaction mixture is poured or percolated into the mould 401. Figure 5 illustrates a construction article 570 made in accordance with Example 1 below, using a cylindrical mould, after 3 (570a), 6 (570b), and 9 (570c) injection / precipitation cycles.

[0362] Figure 6 shows a construction article 670 made according to the present method according to another embodiment, which in this embodiment is in the form of a conventional brick. The brick was prepared using a surface percolation technique. The reaction mixture was allowed to drain freely through the sand (contained within a silicone mould) under gravity, and this was repeated for 6 treatment cycles. The urea concentration was 60 g / l, CaCI_2 111 g / l and soybean concentration 50 g / l. All treatment cycles was carried out at 20°C and atmospheric pressure.

[0363] Figures 7a and 7b show X-ray computed tomography (XCT) images of an article 671 made in accordance with Example 1 below before precipitation (Fig 7a), and of the article 672 after precipitation (Fig 7b). Figure 7c show an X-ray computed tomography (XCT) image of the article 672 of Figure 7b, with precipitated calcite 673 coloured highlighted in colour, and demonstrating that the calcite consolidates the particles of sand 674.

[0364] It will be understood that the present embodiments are provided by way of example only, and that various modifications can be made to the present embodiments without departing from the scope of the invention.

[0365] Examples

[0366] Example 1 :

[0367] Preparation of high strength, lightweight bio-concrete via soybean EICP

[0368] A soybean enzyme solution was prepared by grinding dried soybeans to <212 pm, stirring at 100 g / L in DI water for 30 minutes, then adding 10 g / L gypsum (calcium sulphate dihydrate), and stirring for a further 5 minutes. After resting for 1 hour to allow coagulation of soybean curds, the solution was centrifuged (6000 rpm for 8 minutes) and filtered to <1 pm, yielding a clear enzyme solution. The cementation solution for soybean EICP treatment was prepared by dissolving 2.0M urea and 2.0M CaCh in de-ionized water. The two solutions (enzyme, and urea / CaCh) were mixed at a 1 :1 ratio immediately prior to injection.

[0369] A plastic cylinder (2.7 cm diameter x 5.5 cm height) was filled with quartz sand (grain diameter 212-297 pm) pre-mixed with 10 wt% added water content. 1 pore volume of combined biocementation fluid (15ml) consisting of 60.06 g / l urea, 110.98 g / l CaCI2 and 50g / l soybean urease was fed through a bottom inlet port at a flow rate of 17.5 ml / min. Flow was then turned off and the reaction allowed to proceed over 24 hours at 20°C and atmospheric pressure. This treatment strategy was repeated for a total of 25 cycles over 25 days.

[0370] After 25 treatment cycles the sample was removed from the plastic cylinder and dried at 50°C for 7 days.

[0371] Testing of the Prepared Article

[0372] The testing protocol consisted of analysis via x-ray computed tomography (see Figs 6(a)-6(c)), thermal conductivity measurements, hydraulic conductivity, and unconfined compressive strength tests. The unconfined compressive strength (UCS) was assessed by applying a constant force of 0.1 N / mm2 / s until the sample failed. The thermal conductivity of the treated sample was ~1 .5 W / m K, hydraulic conductivity 0.005 cm / s, and UCS ~20 N / mm2. Notably, the latter is higher than any reported values in the literature, despite retaining some degree of permeability. The sample had dry density of 1.7 g / cm3which is approximately 70% that of equivalent strength conventional concrete.

Claims

CLAIMS:1 . A method of preparing a calcium carbonate compound, the method comprising:(i) reacting urea with an enzyme and a precipitating compound, wherein the precipitating compound comprises or consists of calcium chloride, to yield calcium carbonate and ammonium chloride;(ii) reacting the ammonium chloride to yield hydrogen chloride and ammonium hydroxide or ammonia;(iii) performing a step comprising: either (iii-a1) reacting a calcium-containing mineral with the hydrogen chloride to yield the calcium chloride, wherein the calcium-containing mineral comprises calcium silicate; and when step (ii) yields ammonium hydroxide then (iii-a2) degassing the ammonium hydroxide to yield ammonia; or(iii-b1) reacting a calcium-containing mineral with the ammonium hydroxide to yield calcium hydroxide and ammonia, wherein the calcium- containing mineral comprises calcium silicate, and (iii-b2) reacting the calcium hydroxide and the hydrogen chloride to yield the calcium chloride;(iv) reacting the ammonia produced in step (ii) or step (iii) with carbon dioxide to yield an ammonium salt, wherein the ammonium salt comprises or consist of one or more of ammonium carbamate, ammonium bicarbonate and ammonium carbonate; and(v) reacting the ammonium salt to yield the urea.

2. A method according to claim 1 , wherein step (i) - (v) are carried out sequentially.

3. A method according to any one of the preceding claims, wherein step (i) comprises precipitating the calcium carbonate compound.

4. A method according to any one of the preceding claims, wherein the enzyme used in step (i) comprises a urease and / or a source thereof.

5. A method according to claim 4, wherein the enzyme comprises or consists of an urease obtainable from soybeans (Glycine max) and / or jack beans (Canavalia ensiformis).

6. A method according to any one of the preceding claims, wherein step (i) comprises providing a first reaction mixture comprising the urea, the enzyme and the precipitating compound, in a container.

7. A method according to claim 6, wherein the first reaction mixture and / or the container further comprises a particulate material.

8. A method according to any one of the preceding claims, wherein the method comprises reiterating step (i) multiple times.

9. A method according to any one of claims 1 to 8, wherein step (ii) comprises performing hydrolysis of the ammonium chloride produced in step (i) to yield hydrogen chloride and ammonium hydroxide, and wherein step (iii) comprises step (iii-a1) reacting the calcium silicate with the hydrogen chloride produced in step (ii) to yield the calcium chloride and silica; and step (iii-a2) degassing the ammonium hydroxide produced in step (ii) to yield ammonia.

10. A method according to any one of claims 1 to 8, wherein step (ii) comprises sublimating the ammonium chloride produced in step (i) to yield hydrogen chloride and ammonia, and wherein step (iii) comprises (iii-b1) reacting the calcium silicate with the ammonium chloride produced in step (ii) to yield calcium hydroxide, silica and ammonia, and (iii-b2) reacting the calcium hydroxide produced in step (iii-b1) and the hydrogen chloride produced in step (ii) to yield the calcium chloride.

11. A method according to claim 9, wherein step (iv) comprising reacting the ammonia produced in step (iii).

12. A method according to claim 10, wherein step (iv) comprising reacting the ammonia produced in step (ii).

13. A method according to any preceding claim, wherein step (iv) comprises reacting carbon dioxide fed from an external source.

14. A method of preparing a calcium carbonate compound, the method comprising:(i) reacting urea with an enzyme and a precipitating compound, wherein the precipitating compound comprises or consists of calcium chloride, to yield calcium carbonate and ammonium chloride;(ii) reacting the ammonium chloride to yield hydrogen chloride and ammonium hydroxide or ammonia;(iii) performing a third step comprising:(iii-a1) reacting a calcium silicate material with the hydrogen chloride to yield the calcium chloride and silica; and when step (ii) yields ammonium hydroxide then (iii-a2) degassing the ammonium hydroxide to yield ammonia;(iv) reacting the ammonia produced in step (ii) or step (iii) with carbon dioxide to yield an ammonium salt, wherein the ammonium salt comprises or consist of one or more of ammonium carbamate, ammonium bicarbonate and ammonium carbonate; and(v) reacting the ammonium salt to yield the urea.

15. A method of preparing a calcium carbonate compound, the method comprising:(i) reacting urea with an enzyme and a precipitating compound, wherein the precipitating compound comprises or consists of calcium chloride, to yield calcium carbonate and ammonium chloride;(ii) reacting the ammonium chloride to yield hydrogen chloride and ammonium hydroxide;(iii) performing a step comprising (iii-b1) reacting a calcium silicate material with the ammonium hydroxide produced in step (ii) to yield calcium hydroxide and ammonia, and (iii-b2) reacting the calcium hydroxide and the hydrogen chloride to yield the calcium chloride;(iv) reacting the ammonia produced in step (iii) with carbon dioxide to yield an ammonium salt, wherein the ammonium salt comprises or consist of one or more of ammonium carbamate, ammonium bicarbonate and ammonium carbonate; and(v) reacting the ammonium salt to yield the urea.

16. A method of preparing a calcium carbonate compound, the method comprising:(i) reacting urea with an enzyme and a precipitating compound, wherein the precipitating compound comprises or consists of calcium chloride, to yield calcium carbonate and ammonium chloride;(ii) performing a step comprising: (ii-a1) reacting the ammonium chloride with sodium hydroxide to yield sodium chloride and ammonia; and(ii-a2) reacting the sodium chloride to yield hydrogen chloride and the sodium hydroxide;(iii) reacting a calcium-containing mineral with the hydrogen chloride produced in step (ii-a2) to yield the calcium chloride;(iv) reacting the ammonia produced in step (ii-a1) with carbon dioxide to yield an ammonium salt, wherein the ammonium salt comprises or consist of one or more of ammonium carbamate, ammonium bicarbonate and ammonium carbonate; and(v) reacting the ammonium salt to yield the urea.

Images