Method for producing green cement

Abstract

The present invention relates to a method for producing geopolymer cement comprising the following steps: selection of rock, grinding and drying of the rock, leaching to form two alkaline activators, filtration, calcination, thermal shock, silicate production, drying using waste heat, grinding and homogenisation, and, finally, the formation of dry geopolymer cement. Consequently, the method disclosed here offers several advantages over the prior art, such as: energy savings, reduced reagent costs, simplified material processing, the reuse of industrial facilities used for Portland cement production, reduced CO2 emissions, and more efficient geopolymerisation. The proposed method also offers flexibility in the choice of rock as a raw material, whilst contributing to environmental sustainability by using natural resources efficiently and reducing the use of conventional alkaline activators.

Description

[0001] Descriptive Report of the Invention Patent for: "METHOD FOR PRODUCING GREEN CEMENT".

[0002] Field of Invention

[0003]

[0001] The present invention belongs to the field of materials science, and relates specifically to a method of producing geopolymer cement.

[0004] Background of the Invention

[0005]

[0002] Cement, since its origins in ancient civilizations, has evolved significantly over the centuries. In Ancient Egypt (3000 BC), a mixture of lime and gypsum was used as a binder in the pyramids. In Mesopotamia (2000 BC), bitumen and lime were employed in monumental constructions. The Greeks (500 BC) and Romans (200 BC) introduced advanced techniques, with the Romans developing pozzolanic cement, a mixture of lime and volcanic ash used in works such as the Colosseum.

[0006]

[0003] In Medieval Europe, the use of lime mortar re-emerged in Gothic cathedrals. In 1756, John Smeaton rediscovered the importance of hydrated lime. However, it was Joseph Aspdin, in 1824, who revolutionized the sector by patenting Portland cement, the basis of modern cement. During the Industrial Revolution, this material was mass-produced, driving major infrastructure projects such as the Hoover Dam (1889) and the US Highway System (1956).

[0004] In the 20th century, reinforced concrete enabled new forms of construction. In the 21st century, the focus is on sustainable alternatives, such as green cement, with less environmental impact. The evolution of cement, therefore, has been fundamental to the advancement of civil construction, and there is a continuous need for adaptation to sustainability demands.

[0007]

[0005] Traditional Portland cement, widely used in civil construction, is known for its significant environmental impact, mainly due to CO2 emissions during its production. In contrast, geopolymer cement emerges as an ecological alternative, presenting significant advantages in terms of sustainability and material efficiency.

[0008]

[0006] Portland cement is the most widely used hydraulic binder in the world, with global production exceeding 4.1 Gt per year. It is characterized as a fine, powdery material of gray or white color that, when mixed with water, forms a paste that hardens and transforms into a solid, stone-like substance due to chemical hydration processes. The hydration of Portland cement is a complex exothermic reaction between clinker compounds, calcium sulfate, mineral additives, and water. This reaction is directly influenced by several factors, such as the clinker phase composition, fineness, hydration temperature, water / binder ratio, curing conditions, among others. Consequently, the strength and durability of the final product are also directly influenced by these factors.The main application of Portland cement is as a binder in the production of concrete, which is the most widely used composite material in the construction industry worldwide due to its outstanding adaptability, wide availability of raw materials, and low maintenance costs.

[0009]

[0007] Portland cement manufacturing consists of two stages. In the first stage, clinker is produced by calcining a mixture of limestone and clay or shale in a rotary kiln at approximately 1450°C. In the second stage, the clinker is ground with about 5% calcium sulfate (Equations 1 to 6). This process forms the four main constituent phases of Portland cement clinker: dicalcium silicate (C2S), tricalcium silicate (C3S), tricalcium aluminate (C3A), and tetracalcium aluminate (C4AF). Calcium sulfate (CSH2) is added during grinding.

[0010] Limestone → CaO (1) Clay → SiO2 + Al2O3 + Fe2O3 (2) Clay + Limestone → 1450°C 3CaO.SiO2(C3S) 45%-60% of clinker (3) Clay + Limestone → 1450°C 2CaO.SiO2(C2S) 15%-30% of clinker (4) Clay + Limestone → 1450°C 3CaO.Al2O3(C3A) 6%-12% of clinker (5) Clay + Limestone → 1450°C 4CaO.Al2O3.Fe2O3(C4AF) 6%-8% of clinker

[0011]

[0012]

[0008] The clinkerization process is responsible for 5% to 8% of total global CO2 emissions, since approximately 900 kg of CO2 are released per ton of cement produced. Of this total, about 50% comes from the decarbonation of limestone in the kiln, and the remainder is distributed among fossil fuels for calcination, excavations for raw material extraction, transportation, and grinding of materials.

[0013]

[0009] Portland cement is the concrete component with the worst environmental impact in terms of CO2 emissions. Therefore, the strategy used by cement producers to reduce environmental impact involves the development of composite cements containing a lower clinker content. Strategies for reducing clinker content require its partial replacement with fine materials with favorable chemical and mineralogical compositions. The incorporation of these fines enables an increase in the degree of hydration and particle packing in the cement matrix. However, to ensure the physical and mechanical properties of the matrix, a considerable clinker content is still necessary in composite cements.

[0014]

[0010] In this context, experts in the field of materials science have been seeking to develop more sustainable alternatives to Portland cement. Among these alternatives is geopolymer cement.

[0015]

[0011] Geopolymer is an inorganic material that is formed through the chemical reaction of aluminosilicate precursors (SiO2 and Al2O3) with alkaline activators (alkali metal hydroxides from groups IA and 1B). These alkaline agents react with the silicates (SiO4) and aluminates (AlO4) present in the material, forming new compounds called aluminosilicates. The SiO4 and AlO4 units polymerize, forming the three-dimensional network of aluminosilicates, known as Geopolymer.

[0016]

[0012] Compared to Portland cement, geopolymer cement offers:

[0017]

[0013] (i) Superior Mechanical Properties: Geopolymer cement is recognized for its exceptional mechanical strength which can surpass that of Portland cement, making it suitable for demanding structural applications.

[0018]

[0014] (ii) Greater Durability: Geopolymer cement exhibits greater durability in adverse environments, including resistance to acids, sulfates and thermal variations, contributing to a longer service life for structures.

[0019]

[0015] For example, Chinese patent CN113773028 discloses a geopolymer concrete composition and its preparation method. The invention aims to improve the quality and consistency of geopolymer concrete, offering a more viable and sustainable alternative. The document provides a specific formula for mixing components, including aluminum- and silicon-rich precursors and alkaline solutions.

[0020]

[0016] US Patent 10315952 discloses a solid component activator for use in a geopolymer cement containing a silico-aluminate material comprising a mixture of sodium silicate and sodium carbonate to activate the geopolymer cement by increasing the reactivity of the silico-aluminate material in the geopolymer cement.

[0021]

[0017] Document WO2022 / 226419 discloses methods and compositions for the production of alkali-activated cements, including details on the alkaline solutions used, the formulation of pre-geopolymer materials, and processing conditions. The document highlights improvements compared to traditional methods, such as greater activation efficiency and better cement property performance. Environmental and economic benefits are also discussed, including reduced CO2 emissions and the use of industrial waste as raw materials.

[0018] However, existing geopolymer cement production methods still present many challenges, including: the need to purchase alkaline activating reagents, such as NaOH and KOH, which increases the cost of the process and the dependence on third-party inputs; high energy consumption, since conventional methods involve steps such as heat treatment in furnaces or autoclaves; restrictions regarding raw materials, as conventional methods use inputs that need to meet strict composition criteria, limiting the flexibility of the process and making it less accessible, especially in regions where these materials are not available; demand for new industrial facilities, since the production of geopolymers may require specialized industrial infrastructure; the need for additional drying processes; high CO2 emissions, among others.

[0022] Summary of the Invention

[0023]

[0019] The present invention consists of a method for producing geopolymer cement comprising steps of rock selection, grinding and drying of the rocks, leaching to form two alkaline activators, filtration, calcination, thermal shock, silicate production, drying through residual heat, grinding and homogenization and, finally, formation of dry geopolymer cement.

[0020] Thus, the method disclosed here presents several advantages over the state of the art, such as: energy savings through the use of residual heat and optimization of other energy resources; reduction of reagent costs, using more economical methods of producing alkaline activators, such as sodium silicate; simplification of material treatment, while maintaining process efficiency; reuse of industrial facilities used for Portland cement production, eliminating the need for large investments in new infrastructure; reduction of CO2 emissions, making the process more sustainable and compliant with the Net Zero agenda; and more efficient geopolymerization, resulting in faster and more effective production, with high-quality products.The proposed method also offers flexibility in the choice of rocks as raw material, in addition to contributing to environmental sustainability by using natural resources efficiently and reducing the use of conventional alkaline activators.

[0024] Brief Description of the Figures

[0025]

[0021] Figure 1 is the flowchart of the geopolymer cement production method described in the present invention.

[0026] Detailed Description of the Invention

[0022] This document discloses a method for producing geopolymer cement comprising the following steps:

[0027] i) selection of rocks for precursors and selection of rocks for alkaline activators, and / or multiple rocks for precursors and alkaline activators;

[0028] ii) grinding and drying of rocks for precursors; iii) leaching of rocks for alkaline activators in alkaline solution to form two alkaline activators;

[0029] iv) filtering the product obtained in step iii) of leaching, resulting in non-soluble residues and an alkaline solution;

[0030] v) calcination of the non-soluble residues obtained in step iv) of filtration and of the ground and dried product obtained in step ii) of grinding and drying;

[0031] vi) thermal shock of the product obtained in step v) in a strong alkaline base solution, wherein said strong alkaline base solution comprises the alkaline solution obtained in the filtration step iv);

[0032] vii) silicate production;

[0033] viii) drying through residual heat;

[0034] ix) grinding and homogenization, with the additional addition of alkaline activator and amorphous silica or amorphous aluminate silica; and

[0035] x) formation of dry geopolymer cement.

[0023] In a specific embodiment, the precursor rocks comprise minerals bearing aluminum and silicon oxides; the alkaline activator rocks comprise minerals containing sodium (Na), potassium (K), calcium (Ca), and magnesium (Mg), and carbonates; and the multiple rocks for precursors and alkaline activators comprise minerals bearing aluminum and silicon oxides and minerals containing sodium (Na), potassium (K), calcium (Ca), and magnesium (Mg), and carbonates.

[0036]

[0024] In another embodiment, the grinding and drying stage of the rocks for precursors results in a particle size distribution with d90 preferably situated in the range between 0.040 mm and 0.050 mm.

[0037]

[0025] Preferably, the leaching comprises the encapsulation of carbonate and the formation of a first alkaline activator N(OH)xe and a second alkaline activator Mx.N.(CO3)2•x(H2O), where M and N are metallic cations that can vary between alkali or alkaline-earth metals and ex is an integer from 1 to 3.

[0038]

[0026] In one specific embodiment, calcination occurs between 300°C and 1300°C.

[0039]

[0027] In another embodiment, the alkaline solution used in the thermal shock comprises additional alkaline hydroxides such as NaOH, CaOH, MgOH, KOH, preferably NaOH.

[0028] Preferably, the silicate production step consists of the reaction of available alkaline agents, such as Ca(OH)2, NaOH, KOH or Mg(OH)2, with the amorphized silica generated in the thermal shock.

[0040]

[0029] In a specific embodiment, after drying by means of residual heat, the grinding and homogenization step is carried out by adding amorphous silica or amorphous silico aluminate, as well as between 3% and 10% of alkaline activator comprising alkali metal hydroxides (IA and 1B), preferably between 5% and 7.5% of additive, and preferably in which sodium hydroxide (NaOH) is the alkaline activator.

[0041]

[0030] In another preferred embodiment, the grinding step additionally comprises the addition of calcium (CaO) and magnesium (MgO) oxides.

[0042] Rocks for precursors and activators

[0043]

[0031] The first step of the proposed method consists of choosing suitable rocks for the generation of alkaline precursors and activators.

[0044]

[0032] Choice of Rocks for Precursors: rocks rich in Aluminum and Silicon Oxides - selection of rocks or their supergene alterations, bearing aluminum oxides (Al2O3) and silicon oxide (SiO2). The selection of these rocks is fundamental to guarantee a base rich in siliceous and aluminiferous components, crucial in the formation of geopolymeric structures. Table 1 below presents the various possibilities for choosing rocks for precursors.

[0045]

[0033] Table 1: Rocks for precursors

[0046] Rock Minerals Chemical Formula

[0047] Quartz SiO2

[0048] Feldspar

[0049] alkaline: KA1S Í3O8

[0050] Orthoclásio

[0051] Microcline Granite KAIS Í3O8

[0052] NaAlSi3O8 or (Na 10.9 ,Here 0-0.1 Al 0-0.1 Yes 1-0.9 )Si2O8Plagioclase (Na, Ca ) Al (Si, Al ) Si2O8Feldspar

[0053] potáss ico: KA1S Í3O8

[0054] Orthoclass io

[0055] Microcline KA1S Í3O8

[0056] Gnaisse Plagioclase (Na, Ca ) Al ( Si, Al ) Si2O8

[0057] Fourth zone SiO2

[0058] K (Mg, Fe 2 + )3A1S Í3O 10 (OH, F )2OU K (Mg, Fe Biotite 2 + )3

[0059] (Al, Faith 3 + ) Si3O 10 ( OH, F )2Fourth zone SiO2

[0060] Feldspar

[0061] alkaline: KA1S Í3O8

[0062] Orthoclass io

[0063] Microcline KA1S Í3O8

[0064] Rhyolite

[0065] AlSi3O8ou (Na 10.9 ,Ca 0-0.1 )Al(Al 0-0.1 ,Yes 1-0.9 )Si2O8Plagioclase (Na, Ca ) Al ( Si, Al ) Si2O8

[0066] K (Mg, Fe

[0067] K(Mg,Fe 2+ )3AlSi3O 10 (OH,F)2ou K(Mg,Fe 2+ )3

[0068]

[0069] (Al, Faith 3 + ) Si3O10 ( OH, F )2

[0070]

[0034] Choice of Rocks for Alkaline Activators: Minerals containing sodium (Na), potassium (K), calcium (Ca), and magnesium (Mg) are used in the production of alkaline activators. They play a crucial role in the solubilization and reaction of the siliceous and aluminous components of the starting materials. Table 2 presents possibilities for rocks containing sodium (Na), potassium (K), calcium (Ca), and magnesium (Mg). In addition, rocks containing carbonates (CO3), such as calcite (CaCCA), dolomite (CaMg(CO3)2), aragonite (CaCO3), magnesite (MgCCh), ankerite (Ca(Mg,Fe)(CO3H), and etrona / sodium carbonate (NaHCO3), are used to generate new alkaline activators. This practice can reduce the consumption of conventionally used activators. Table 3 presents possibilities for rocks rich in carbonate minerals.

[0071]

[0035] Table 2: Rocks for alkaline activators containing sodium (Na), potassium (K), calcium (Ca), and magnesium (Mg)

[0072] Mineral Rock Chemical Formula Wollastonite CaSiO3

[0073] Magnesite MgCO3

[0074] NaAlSi3O8 or (Na 10.9 ,Here 0-0.1 Al 0-0.1 Yes 1-0.9 )Si2O8Orthoclase KAlSi3O8Microcline KAlSi3O

[0075]

[0076] 8

[0077]

[0036] Table 3: Rocks for alkaline activators rich in carbonate minerals

[0078] Rock Minerals Chemical Formula Calcite CaCO3

[0079] Limestone

[0080] Dolomite CaMg ( CO3)2

[0081] Quartz SiO2

[0082] NaAlSi3O8 or (Na 10.9 ,Here 0-0.1 Al 0-0.1 Yes 1-0.9 )Si2O8Diops idio CaMgSi2O6or Ca (Mg, Fe ) Si

[0083]

[0084] 2O6 Ca2(Mg, Fe 2 + )5Si8O 22( OH )2ou

[0085]

[0086] ( Ca, Na )2(Mg, Fe 2+ , Al )5Si8O 22 ( OH )2Hornblende-(Na,K) 0-1 Ca2(Mg,Fe 2+ ,Faith 3+ ,Al,Ti)5(Si6Al2)O 22 (OH,O)2Coarse Ca3Al2(SiO4)3Andradite Ca3Fe 3+ 2(SiO4)3Titanite CaTiSiO5or CaTiSiO4( 0, OH, F )

[0087] Ca2Al2( Fe 3 + , A1 ) ( Si2O7) ( SiO4) O ( OH ) or Epidote

[0088] Ca2( Fe, Al ) Al2( SiO4) ( Si2O7) O ( OH ) Olivine (Mg, Fe )2SiO4

[0089] Talc Mg3Si4O 10 (OH)2

[0090] TO 5-6 Z4O 10 (OH)8, where A = Al, Fe 2+ , Faith 3+ , Li, Mg, Mn, Ni, and Z = Al, Si, Fe 3+ .

[0091] Magnesite MgCO3Hydromagnesite Mg5(CO3)4(OH)2·4H2O

[0092]

[0093] Hydrotalcite Mg6Al2(OH) 16 CO3·4H2O

[0094]

[0095]

[0037] Multiple Rock Selection for Alkaline Precursors and Activators: rocks that simultaneously contain sodium (Na), calcium (Ca), magnesium (Mg), potassium (K), aluminum oxides (Al2O3), and silicon dioxide (SiO2). These rocks are ideal for the integrated production of precursors and activators.

[0096]

[0038] Table 4: Multiple rocks for alkaline precursors and activators

[0097] Rock Minerals Chemical Formula

[0098] Olivine (Mg, Fe) 2SiO4

[0099] (XYZ2O6) where X: Na + , Ca 2 + , Mn 2 + , Faith 2 + , Mg 2 + Li + ;

[0100] Pyroxene Basalt Y:Mn 2 + , Faith 2 + , Mg 2 + , Faith 3 + Al 3 + , 0r 3 + Ti 4+ Z:

[0101] Yes 4+ Al 3 +

[0102] Plagioclase (Na, Ca) Al (Si, Al) Si2O8Plagioclase (Na, Ca) Al (Si, Al) Si2O8

[0103] K (Mg, Fe 2 + )3AlSi3O 10 ( OH, F)2ou K (Mg, Fe Biotite 2 + )3

[0104] (Al, Fe 3 + ) Si3Oio ( OH, F)2

[0105] Gabbro Augita (Ca, Na) (Mg, Fe, Al, Ti) (Si, Al)2O6

[0106] Olivine (Mg, Fe )2SiO4

[0107] (Na, K)0-iCa2(Mg, Fe 2 + , Faith 3 + , Al, Ti ) 5 ( Si6Al2)8O Hornblende 22

[0108]

[0109] ( OH, O )2

[0039] In the context of the process described here, calc-silicate rocks stand out as an important innovation due to their diverse mineral composition, which makes them highly suitable for both the generation of precursors and the production of alkaline activators. These rocks are particularly rich in minerals such as pyroxene, amphibole, quartz, orthoclase, titanite, and garnet, which provide a wide range of essential elements, including sodium (Na), calcium (Ca), magnesium (Mg), potassium (K), aluminum (Al), and silica (Si), essential for geopolymer synthesis.

[0110]

[0040] Pyroxene, a fundamental mineral in calc-silicate rocks, contains elements such as sodium, calcium, magnesium, and iron in its structure, which contribute significantly to the alkaline activation of materials, promoting the solubilization of siliceous and aluminous components. The general formula for pyroxene is (XYZ2O6), where X can include Na. + , Ca 2 + , Mg2 + , and Y contains Mn 2 + , Faith 2 + , Mg 2 + , and Z represents Si 4+ or Al 3 + This reinforces its versatility and dual role in supplying precursors and activators.

[0111]

[0041] Amphibole, another essential mineral, also has a complex structure that includes elements such as calcium, sodium, magnesium, and aluminum, present in its overall formula, contributing directly to the creation of a highly reactive and stable geopolymer matrix.

[0112]

[0042] Furthermore, the presence of quartz (SiO2) and orthoclase (KAISiSo) in calc-silicate rocks provides sources of silica and aluminum, key elements for the formation of geopolymer precursors. These minerals play a critical role in the final structure of the material, giving it high strength and durability.

[0113]

[0043] Finally, titanite (CaTiSiOc) and garnet (AlB2Si3O12), minerals containing calcium and titanium, as well as other elements such as iron, magnesium and aluminum, are able to act both in stabilizing the geopolymer structure and in activating other mineral phases, promoting the formation of a more robust and efficient final product.

[0114]

[0044] The use of calc-silicate rocks in the geopolymer process, such as those in Table 5, provides an integrated approach that reduces the need to add external sources of alkaline activators, simplifying the production process and contributing to a more sustainable and economical solution.

[0115]

[0045] Table 5: Calc-silicate rocks

[0116] Rock Minerals Chemical Formula

[0117] (XYZ2O6) where X: Na + , Ca 2 + , Mn 2 + , Faith 2 + Pyroxene Mg 2 + Li + Y: Mn 2 + , Faith 2 + , Mg2 + , Faith 3 + Al 3 + , Rocks Cr 3 + Ti 4+ Z: Yes 4+ Al 3 + calc-silicates W0-1X2Y5Z8O22 (OH, F) 2 • Where W: Na + and K + ; X:

[0118] Amphibolium Ca 2+ In + , Mn 2+ , Faith 2+ , Mg 2+ and Li + Y: Mn 2+ ,

[0119] Faith 2+ , Mg 2+ , Faith 3+ Al 3+ and Ti 4+ Z: Yes 4+ and Al 3+ .

[0120]

[0121] Quartz SiO2

[0122] Orthoclase KA1SÍ3O8

[0123] Titanite CaTiSiO5or CaTiSiO4(O,OH,F)

[0124] A3B2SÍ3O12, in which A = Fe, Ca, Mn or Mg; and Granada

[0125]

[0126]

[0127] B = Al, Fe, Ti or Cr.

[0128]

[0046] The use of alkaline activators represents between 30% and 60% of the geopolymer. As an innovation, the production of other, lower-cost activators is proposed. Normally, sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) are used. Alternatively, the present invention proposes the use of other alkali metal hydroxides from groups IA and 2A, specifically magnesium hydroxide (Mg(OH)2) and calcium hydroxide (Ca(OH)2). These hydroxides can act separately or in combination with sodium hydroxide (NaOH) and sodium silicate (Na2SiO2).

[0129]

[0047] The choice of rocks for alkaline precursors and activators (SiO2 and Al2O2), as well as rocks rich in carbonate minerals (CO2) and multiple rocks that simultaneously contain sodium (Na), calcium (Ca), magnesium (Mg), potassium (K), aluminum oxides (Al2O2) and silicon dioxide (SiO2), can occur in different geological environments. This allows the location of sources close to consumption sites, minimizing the distance between cement producers and consumers.

[0130]

[0048] Innovation in material selection methods and component formulation for geopolymer production not only optimizes the manufacturing process but also contributes to environmental sustainability by using natural resources efficiently and reducing the use of conventional alkaline activators.

[0131] Drying and Grinding

[0132]

[0049] The selected rocks containing Na, Ca, Mg, K, Al and Si are subjected to drying and grinding to achieve the desired particle size, characterized by d90 preferably between 0.040 and 0.050 mm. Fine grinding is crucial to increase the surface area of ​​the material, improving subsequent leaching and calcination processes.

[0133] Leaching of carbonates

[0134]

[0050] To inhibit CO2 generation, carbonate (CO3)-bearing rocks are leached in an alkaline solution.

[0135]

[0051] For rocks containing carbonates (M.CO3, where M is a metallic cation of an alkali or alkaline earth metal), during the calcination process, these carbonates (M.CO3) decompose into oxides (M.O) and carbon dioxide (CO2), releasing greenhouse gases. To avoid the formation of CO2 during calcination, the method disclosed here involves leaching these rocks with alkaline agents containing the hydroxyl radical (OH), such as sodium hydroxide (NaOH), magnesium hydroxide (Mg(OH)2), calcium hydroxide (Ca(OH)2), and other compounds containing the hydroxyl radical (OH). The reactions involved are described below: xM.OH + N.CO3 + H2O → Mx.CO3 + N(OH) x (7)

[0136]

[0052] In Equation 7, M and N are metallic cations that can vary between alkali or alkaline earth metals, e.g., is an integer from 1 to 3, indicating the number of hydroxide ions that the N cation can support, depending on its charge. In the aforementioned Equation (7), the alkali metal hydroxide reacts with the metal carbonate N.(CO3) to form a new carbonate (MX.CO3) and a new hydroxide (N(OH)x). The reaction continues with the carbonate generated (Mx.COs) in the first reaction (1) reacting with the first carbonate N.CO3. The objective of this reaction is to avoid the release of CO2, encapsulating the carbonates during the process.

[0137] Formation of two alkaline agents

[0138]

[0053] The leaching of carbonates is associated with the formation of two alkaline agents. In the second reaction of the geopolymer formation process (Equation 8), carbonates (CO3-bearing minerals) react with Mx.(CO3), where M represents a metallic cation. This reaction leads to the formation of Mx.N.(CO3)2.x(H2O), a hydrated double salt that encapsulates the carbonate (CO3), which is responsible for the generation of CO2. The cations involved in the formation of this double salt are M and N, which can vary between alkali or alkaline earth metals, and the anion is CO3. Furthermore, x is an integer from 1 to 3. In this reaction, the encapsulation of CO3 that would generate CO2 occurs:

[0139] M x CO3 + N CO3 + H2O → M x .N(CO3)2.x(H2O) (8)

[0140]

[0054] Energy and Reaction Conditions: This is an endothermic reaction, with a Gibbs free energy of 255.2 kJ, indicating that it absorbs heat from the environment. Due to its endothermic nature, the reaction requires constant stirring and heating to proceed efficiently. Stirring can vary between 100 and 700 RPM, preferably between 200 and 500 RPM. The temperature must be carefully controlled to provide sufficient energy and allow the reaction to occur efficiently. Heating can vary between 50°C and 200°C, preferably between 80°C and 120°C. It is important to note that the temperature in leaching is a result of thermal shock, since the solution will be recirculated for leaching and thermal shock, and vice versa. That is, this occurs because the same solution will be applied to the thermal shock, raising its temperature during the process and affecting the leaching temperature.

[0141]

[0055] Activation with Alkaline Agents and Geopolymer Formation: the double hydrate salt, Mx. N. (CO3) 2.x (H2O), is activated by the addition of an alkaline agent containing the hydroxyl radical (OH). This agent can be, for example, the N (OH) x obtained in the first reaction. The presence of this alkaline agent is crucial to trigger the formation of the geopolymer. Thus, the method of the present invention proposes the formation of two alkaline agents, first in the formation of N (OH) x from reaction (7), generating a first alkaline activator, and the second in the formation of Mx. N. (CO3) 2 • x (H2O) from reaction (8), generating a second alkaline activator.

[0142]

[0056] The alkaline activation process promotes the polymerization of the SiO4 and AlO4 units present in the material, leading to the formation of a three-dimensional network of aluminosilicates, which is the basic structure of a geopolymer.

[0143] Filtration

[0144]

[0057] After the leaching step, the resulting solution, which contains the double hydrate salt, is separated from an insoluble residue. This separation is carried out by filtration, where the solution containing the double hydrate salt is isolated from the solid residue that is free of CO2.

[0145]

[0058] The solid residue, now free of CO2, is sent to the next stage of the process, which is calcination, as are the rocks containing aluminum oxides (Al2O3) and silicon dioxide (SiO2), already ground and dried.

[0059] The liquid fraction obtained in the filtration is an alkaline solution, which will later be used for immersion of the product obtained after calcination.

[0146] Calcination

[0147]

[0060] Calcination occurs between 300°C and 1300°C and is crucial for preparing materials for subsequent chemical activation, enabling the transformation of residual materials into a more reactive form suitable for geopolymer formation.

[0148]

[0061] Preparation for Calcination: the solid residue, which is now free of carbonates (CO3), is sent for calcination. This process also includes rocks that are rich in aluminum oxides (Al2O3) and silicon oxide (SiO2), which are essential for the synthesis of geopolymers.

[0149]

[0062] Calcination Procedure: Calcination is a crucial thermal process carried out at temperatures ranging from 300°C to 1300°C. Ideally, the chosen temperature is slightly higher than the thermal degradation temperature determined by thermogravimetric analysis (TGA).

[0150]

[0063] The main objective of calcination is to eliminate the hydroxyl radicals (OH) present in the materials. This is crucial to prevent rehydration and maintain the chemical stability of the precursors.

[0151]

[0064] Furthermore, the process aims to alter the crystalline structure of the minerals, transforming it into an amorphous form. The amorphization of the minerals is fundamental to increasing the reactivity of the materials, which is essential for the subsequent chemical activation during the synthesis of the geopolymer.

[0152] Thermal shock

[0153]

[0065] Rock Preparation for Thermal Shock: Rocks containing calcium (Ca), magnesium (Mg), potassium (K), aluminum (Al), and silicon (Si), which have already undergone a calcination process in the previous step, are prepared for thermal shock. This thermal treatment aims to raise the temperature of the rocks slightly above the thermal degradation temperature determined by Thermogravimetric Analysis (TGA).

[0154]

[0066] Immersion in Alkaline Solution: After calcination of the precursors (SiO2 and Al2O3), the method disclosed here involves immersion in an alkaline solution of the rocks and residues resulting from the alkaline leaching of CO3-bearing rocks. This alkaline solution is obtained from reactions (7) and (8) described previously, involving compounds such as N(OH)xe Mx.N.(CO3)2.x(H2O), and may also contain calcium, magnesium and sodium hydroxides.

[0155]

[0067] Transformation of Crystalline Structures: During thermal shock, when calcined rocks are immersed in the alkaline solution, their crystalline structures transform into amorphous structures. This alteration is crucial for the reactivity of the material, allowing for a more effective interaction with the components of the alkaline solution.

[0156]

[0068] Silicate Formation: The availability of alkaline agents, such as Ca(OH)2, NaOH, KOH, or Mg(OH)2, combined with the presence of already amorphized silica, promotes the formation of various types of silicates, including sodium silicate. This process presents a new approach to the production of sodium silicates, in addition to conventional methods.

[0157]

[0069] Currently, sodium silicate is traditionally formed by two processes. The first, and most common, involves the reaction between NaOH and SiO2 in an autoclave, under high pressure and temperature conditions. The second process uses alkaline fusion, in which sodium carbonate is melted in refractory furnaces. Therefore, the method described here offers a more efficient alternative, using controlled reactions with alkaline agents and amorphized silica, optimizing production and saving energy compared to traditional methods.

[0158]

[0070] Unlike conventional methods that use air or water cooling, this step of the method consists of using a solution containing alkaline agents to perform the thermal shock. The solution contains N(OH)xe Mx.N.(CO3)2 • x(H2O), and other alkaline hydroxides such as NaOH, CaOH, MgOH, KOH may be added, but NaOH is preferred.

[0159]

[0071] Formation of Geopolymer Compounds: the interaction of elements such as silica (SiO2) and aluminum oxide (Al2O3), present in rocks, with the alkaline solution rich in calcium (Ca(OH)2), magnesium (Mg(OH)2) and sodium (NaOH) hydroxides, facilitates the formation of geopolymer compounds. These compounds are characterized by their robust three-dimensional structures.

[0160]

[0072] Thermal Shock Execution: Thermal shock is performed by raising rocks and other relevant materials to a specific temperature within an alkaline solution. This temperature is carefully chosen to be high enough to facilitate the necessary chemical reactions, but also to ensure that, after separation from the alkaline solution, the materials retain sufficient residual heat. The temperature for thermal shock ranges from 150°C to 500°C. This temperature range is suitable for thermal shock in alkaline solutions, allowing interaction between the activated precursors and the alkaline solution without causing structural damage to the materials. Within this range, chemical reactions occur in a controlled manner. The temperature for thermal shock can be within a more restricted range, from 250°C to 400°C.This range is more common for thermal shock processes in geopolymers and similar materials, being sufficient to induce reactions without risk of component manipulation or excessive heat loss. The preferred temperature range for thermal shock is 325°C to 375°C. This is the ideal temperature range for thermal shock in an alkaline solution, where materials are immersed immediately after roasting. In this range, responses are facilitated, and residual heat is planned, contributing to process efficiency. This preferred range promotes ideal material reactivity and maintains sufficient residual heat for subsequent steps. These temperatures are optimized to maximize the efficiency of the test process and ensure material reactivity without excessive heat loss.

[0161]

[0073] After thermal shock in alkaline solution, the precursor mass is dried using residual heat. Drying is followed by a grinding process with a disintegrating character, preparing the mass for the addition of the chemical activator.

[0162] Silicate production

[0163]

[0074] After thermal shock and before residual heat drying, the method comprises the silicate production step, which takes advantage of the availability of alkaline agents, such as Ca(OH)2, NaOH, KOH or Mg(OH)2, in combination with the amorphized silica generated during the heat treatment. This condition promotes the formation of specific silicates, such as sodium silicate or other silicates, depending on the alkaline agent used.

[0164]

[0075] Specifically, this step results in a form of sodium silicate production that differs from traditional methods. Currently, sodium silicate is formed mainly by two processes: i) reaction of NaOH with SiO2 in an autoclave, using high pressure and temperature; and ii) alkaline fusion with sodium carbonate in refractory furnaces.

[0165]

[0076] Thus, this step stands out for allowing the production of sodium silicate under milder conditions, without the need for an autoclave or alkaline fusion, using silica already amorphized by the thermal shock step and reacting directly with NaOH (or other alkaline hydroxides) in a more controlled environment. This represents a significant advance, as it reduces energy costs and process complexity, while maximizing efficiency in silicate formation, especially sodium silicate.

[0166]

[0077] Furthermore, this approach offers flexibility in the choice of alkaline agent, allowing the production of different types of silicates, such as calcium silicate, potassium silicate or magnesium silicate, depending on the process requirements. The controlled formation of these silicates further improves the reactivity and efficiency of the system, especially in geopolymerization processes.

[0167]

[0078] This step also results in a sustainable method, while aligning the process with geopolymerization without the need for additional high-pressure or alkaline fusion equipment.

[0168] Drying using residual heat

[0169]

[0079] After the silicate production stage, the method involves drying the materials using waste heat. Waste heat is preserved and plays a crucial role, so it must be sufficient to promote the drying of the materials. This is achieved by maintaining a residual temperature that evaporates excess moisture from the materials without the need to apply an additional drying process. This step not only results in energy savings but also simplifies the overall material handling process.

[0170]

[0080] Rapid Cooling After Thermal Shock: After reaching the desired temperature during thermal shock, the materials are rapidly cooled. This rapid cooling is crucial to stabilize the chemical and physical interactions that occurred, transforming the crystalline structure into an amorphous structure. It also prevents rehydration or other reactions that could compromise the quality of the final material.

[0081] Post-Thermal Shock Drying Step: After the thermal shock process in alkaline solution, the residual heat is used to dry the materials. This drying is fundamental to preparing the precursor mass for the next step, ensuring that it is dry and more receptive to the grinding process.

[0171]

[0082] Energy Savings: By utilizing the residual heat generated in the process, there is a significant reduction in energy consumption compared to that required in conventional drying stages. Most of the energy has already been applied during the thermal shock, and the residual heat is sufficient to remove moisture from the materials. This reduces the demand for external energy sources, such as ovens or specialized dryers, making the process more sustainable and less dependent on electricity or fuels.

[0172]

[0083] In an industrial context, this approach is extremely advantageous because it minimizes operational costs related to energy use and simplifies process control, making it more economical and sustainable. Eliminating extra drying steps, while preserving process efficiency, provides greener and more optimized production, with a positive impact on sustainability.

[0173] Grinding and Addition of Additional Activator

[0084] Fine grinding is carried out with the aim of breaking up the precursor mass by adding between 3% and 10% of alkaline activator comprising alkali metal hydroxides (IA and 1B), preferably between 5% and 7.5% activator, with sodium hydroxide (NaOH) being the preferred activator. Grinding not only results in size reduction but also increases the contact surface of the particles, which is fundamental to improving the reactivity of the material.

[0174]

[0085] Thus, in conjunction with grinding, the method described here proposes the extra addition of an alkaline agent containing OH₂ (hydroxide) to the dry mass for eventual adjustment of the composition of the dry geopolymer cement, preferably using NaOH (sodium hydroxide) as the alkaline agent. The incorporation of a source of amorphous silica or amorphous silicoaluminate during the grinding and homogenization process of the mixture is also proposed. These compounds have the function of reacting with the calcium hydroxide [Ca(OH)₂] formed or added in the previous steps, resulting in hydrated calcium silicate (CSH). CSH is the main hydration product generated in the hydration of Portland cement, known for providing densification of the matrix and consequent increase in properties related to mechanical strength and durability.Furthermore, the consumption of free Ca(OH)2 in the matrix prevents the emergence of pathologies related to the exposure of this compound to weathering, which also provides greater durability to the final product.

[0175]

[0086] Solubilization and Activation: With the addition of water to the geopolymer cement, sodium hydroxide, due to its high solubility, facilitates the solubilization of the added alkaline agent. This process is crucial for the solubilization of the precursor during thermal shock.

[0176]

[0087] Initiation of the Chemical Reaction: This alkaline activator is essential to initiate the chemical reaction that forms the three-dimensional network of aluminosilicates, known as a geopolymer. Activation involves the reaction of the alkaline agent with the silicates (SiO4) and aluminates (AlO4) present in the mass.

[0177]

[0088] Geopolymer Formation: the interaction of the alkaline agent with the silicate and aluminate precursors results in polymerization, forming a robust three-dimensional aluminosilicate structure, which characterizes the geopolymer material.

[0178]

[0089] The grinding stage may additionally include the addition of calcium (CaO) and magnesium (MgO) oxides. The combination of sodium silicate with calcium (CaO), magnesium (MgO) oxides and sodium hydroxide (NaOH) presents the following effects:

[0090] - CaO and MgO: increase the reactivity of the system, forming hydrated phases that contribute to the development of the microstructure and the increase in resistance.

[0179]

[0091] - NaOH: raises the pH, accelerating the dissolution of the components and promoting a more complete reaction.

[0180]

[0092] One of the great advantages of this step is the saving of sodium silicate, which is the most expensive item in the process. The strategic combination of sodium silicate with other alkaline agents, such as NaOH, CaO and MgO, allows reducing the amount of sodium silicate needed without compromising reactive efficiency. This significantly reduces production costs, since sodium silicate, being the most expensive input, can be partially replaced by other more accessible components, such as NaOH. This optimizes the use of materials, ensuring a more economical and sustainable process, with lower input costs without losing the quality of the geopolymer produced.

[0181]

[0093] Addition of amorphous silica or amorphous silico aluminate precursors: In addition to the combination of sodium silicate, calcium oxide (CaO), magnesium oxide (MgO) and sodium hydroxide (NaOH), amorphous silica or amorphous silico aluminate precursors can also be added at this grinding stage. These compounds are highly reactive and can act as essential precursors, promoting greater aluminosilicate formation and optimizing the structural properties of geopolymer cement.

[0182]

[0094] Advantages of the Formulation: the addition of an extra alkaline agent and CaO and MgO in the grinding step results in several advantages:

[0183]

[0095] - Flexibility in formulation: the combination of CaO and MgO allows adjustments to the composition to optimize properties such as setting time, strength and durability;

[0184]

[0096] - Microstructure development: the presence of CaO and MgO favors the formation of hydration products, such as calcium silicate hydrate (CSH) and magnesium silicate hydrate (MSH), which are essential for superior mechanical properties;

[0185]

[0097] - Durability and strength: The inclusion of CaO and MgO increases the durability and compressive strength of the material.

[0186]

[0098] Furthermore, the addition of CaO and MgO allows the use of industrial waste, promoting sustainability. Also, depending on specific performance, durability or cost requirements, the choice between using pure sodium silicate or a combination with CaO, MgO and NaOH may vary. This combination is preferable for applications that demand high initial strength and durability.

[0187] Dry Geopolymer Cement

[0099] Starting from a dry material comprising precursors and alkaline agents, geopolymerization will occur with the addition of water, through a dehydration reaction, according to the reactions below:

[0188] Al2SiO3(OH)4 + 4SiO2 + NaOH + H2O Na2.5[SiO2].2[AlO2] + 6H2O (9) 2Ca4SiO5 + 7H2O -> 3CaO.2SiO2.4H2O + 3Ca(OH)2 (10) Advantages and conclusions

[0189]

[0100] The geopolymer cement production method proposed in the present invention comprises the integration of steps such as the optimized selection of precursor and activator source rocks, carbonate leaching, thermal shock, sodium silicate production, residual heat drying, and progressive dehydration geopolymerization. This integration results in an advantageous, sustainable, flexible method that is superior to previously disclosed methods.

[0190]

[0101] The optimized selection of rocks, such as granite and basalt rich in silicon oxides (SiO2) and aluminum oxides (Al2O3), is an essential feature. Unlike the approaches described in the prior art, which deal with the use of minerals in a broader way, this careful selection is based on the reactive and geological properties of the rocks, optimizing the efficiency in the geopolymerization process.

[0191]

[0102] The leaching of carbonates in activating rocks, such as limestone and magnesite, allows the controlled release of alkaline ions crucial for chemical activation. This process offers greater control over the alkaline environment, promoting greater reactivity and quality of the final product.

[0192]

[0103] In the methods disclosed here, thermal shock in alkaline solution amorphizes the mineralogical structure of the precursors, which increases reactivity and makes geopolymerization more efficient. At the same time, geopolymerization by progressive dehydration eliminates dependence on traditional hydration methods, providing the formation of more stable and durable geopolymers with less water dependence.

[0193]

[0104] The production of sodium silicate uses a combination of alkaline agents such as Ca(OH)2, NaOH, KOH or Mg(OH)2 with amorphized silica, which results in a significant saving of sodium silicate, one of the most expensive components of the process.

[0194]

[0105] Residual heat drying utilizes the heat retained after thermal shock to dry materials, eliminating the need for an additional drying step. This method simplifies the process and results in energy savings.

[0195]

[0106] Additionally, the disclosed geopolymer cement production method allows for the integration and use of equipment already available in a Portland cement plant. More specifically, it is possible to utilize the existing feeding structure and rotary kiln in the Portland cement plant, optimizing available resources and reducing the demand for investments in new facilities. The rotary kiln can be used in the calcination stage with lower fuel consumption (due to the reduced temperature compared to the clinkerization process), ensuring greater efficiency in the production process.

Claims

CLAIMS 1. A method for producing geopolymer cement characterized by comprising the following steps: i) selection of rocks for precursors and selection of rocks for alkaline activators, and / or multiple rocks for precursors and alkaline activators; ii) grinding and drying of rocks for precursors; iii) leaching of rocks for alkaline activators in alkaline solution to form two alkaline activators; iv) filtering the product obtained in step iii) of leaching, resulting in non-soluble residues and an alkaline solution; v) calcination of the non-soluble residues obtained in step iv) of filtration and of the ground and dried product obtained in step ii) of grinding and drying; vi) thermal shock of the product obtained in step v) in a strong alkaline base solution, wherein said strong alkaline base solution comprises the alkaline solution obtained in the filtration step iv); vii) silicate production; viii) drying through residual heat; ix) grinding and homogenization, with the additional addition of alkaline activator and amorphous silica or amorphous aluminate silica; and x) formation of dry geopolymer cement.

2. Method according to claim 1, characterized in that: Precursor rocks comprise minerals containing aluminum and silicon oxides; The rocks for alkaline activators comprise minerals containing sodium (Na), potassium (K), calcium (Ca), and magnesium (Mg), and carbonates; and - Multiple rocks for alkaline precursors and activators comprise minerals bearing aluminum and silicon oxides and minerals containing sodium (Na), potassium (K), calcium (Ca), and magnesium (Mg), and carbonates.

3. Method, according to claim 1 or 2, characterized in that the grinding and drying step of the rocks for precursors results in a particle size distribution with d90 preferably situated in the range between 0.040 mm and 0.050 mm.

4. Method, according to any one of claims 1 to 3, characterized in that the leaching comprises the encapsulation of carbonate and the formation of a first alkaline activator N(OH)xe and a second alkaline activator Mx.N.(CO3)2.x(H2O), where M and N are metallic cations that may vary between alkali or alkaline-earth metals and ex is an integer from 1 to 3.

5. Method, according to any one of claims 1 to 4, characterized in that calcination occurs between 300°C and 1300°C.

6. A method according to any one of claims 1 to 5, characterized in that the thermal shock occurs between 150°C and 500°C, preferably 250°C and 400°C, more preferably 325°C and 375°C.

7. A method according to any one of claims 1 to 6, characterized in that the alkaline solution used in the thermal shock comprises additional alkaline hydroxides such as NaOH, CaOH, MgOH, KOH, preferably NaOH.

8. A method according to any one of claims 1 to 7, characterized in that the silicate production step consists of reacting available alkaline agents, such as Ca(OH)2, NaOH, KOH or Mg(OH)2, with the amorphized silica generated in the thermal shock.

9. Method, according to any one of claims 1 to 8, characterized in that, after drying by means of residual heat, the grinding and homogenization step is carried out by adding amorphous silica or amorphous silicoaluminate, as well as between 3% and 10% of an alkaline activator comprising alkali metal hydroxides (IA and 1B), preferably between 5% and 7.5% of additive, and preferably in which sodium hydroxide (NaOH) is the alkaline activator.

10. Method according to claim 9, characterized in that the grinding step additionally comprises the addition of calcium (CaO) and magnesium (MgO) oxides.

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