Belite cement

Abstract

The invention relates to a method for manufacturing a belite cement clinker The method comprises steps of providing raw materials comprising 10 to 90 wt.% green liquor dregs (GLD), and 0 to 50 wt.% bio-based fly ash, based on total dry weight of the raw materials, and heating a mixture comprising the raw materials in a thermal treatment unit by using a process temperature and a residence time. The invention further relates to a belite cement clinker. The invention further relates to a belite cement composition. The invention further relates to method for manufacturing a belite cement composition.

Description

[0001] BELITE CEMENT

[0002] Technical field

[0003] This specification relates to a method for manufacturing a belite cement clinker. This specification further relates to a belite cement clinker. This specification relates to a method for manufacturing a belite cement composition. This specification further relates to a belite cement composition.

[0004] Cement clinker is an intermediary product in the manufacture of a cement. Cement clinker is a solid material that can be produced by sintering e.g. limestone and clay in a cement kiln. Cement clinker can be in a form of nodules.

[0005] Various kinds of cements are known in the industry, such as Portland cement and belite cement.

[0006] Portland cement is a commonly used cement. Portland cement can be fabricated from a cement clinker. A typical temperature for producing Portland cement is approximately 1450-1500 °C.

[0007] Belite cements are cements containing at least belite, typically also alite and calcium aluminates.

[0008] However, there is still a need for novel solutions for obtaining a cement clinker and a cement.

[0009] It is an object of this specification to provide a method for manufacturing a belite cement clinker. It is an object of this specification to provide a belite cement clinker. It is an object of this specification to provide a belite cement composition and a method for manufacturing a belite cement composition. Aspects of the invention are characterized by what is stated in the independent claims. Some preferred embodiments of the invention are disclosed in the dependent claims. These and other embodiments of the invention are disclosed in the description and figures.

[0010] Several industrial side and waste streams are generated in various industrial processes. Conventionally, these industrial side streams have been difficult to utilize as a raw material for a product or as a product.

[0011] Conventionally, virgin raw materials, e.g., limestone, has been used as a raw material for a belite cement.

[0012] Nowadays, producers and end users are looking for environmentally friendly solutions. One of the most challenging production side streams to recycle has been green liquor dregs, created in the soda recovery boiler while burning dissolved wood material. Furthermore, said green liquor dregs (GLD) are typically one of the largest fractions of inorganic residue in kraft pulping processes. Surprisingly, it is possible to replace at least part of the virgin raw materials by using said difficult waste material, i.e., GLD, as a raw material for producing a belite cement.

[0013] Thus, surprisingly, it is possible to replace virgin materials used in a belite cement production with green liquor dregs. In addition to the GLD, the novel belite cement can comprise some other industrial side streams and / or industrial wastes.

[0014] A method for manufacturing a belite cement clinker can comprise the following steps: providing raw materials comprising

[0015] 10 to 90 wt.%, preferably 20 to 80 wt.% (by dry weight) green liquor dregs (GLD), and

[0016] 0 to 50 wt.%, preferably 10 to 40 wt.% (by dry weight) bio-based fly ash, heating a mixture comprising the raw materials in a thermal treatment unit by using a predetermined temperature and a residence time, thereby forming a belite cement clinker. Advantageously, the raw materials comprise 30-80 wt.%, more preferably 40- 70 wt.%, and most preferably 50-60 wt.% green liquor dregs (GLD), based on a total dry weight of the raw materials. Technical effect is that by replacing virgin limestone with green liquor dregs, mining and crushing of non-renewable material can be avoided. Further, by using green liquor dregs instead of limestone, a significantly lower emission of fossil CC ekv is achieved. Further technical effect is that the difficult waste material, i.e., GLD, can be used as a raw material for producing a new product.

[0017] Advantageously, the raw materials comprise 10-45 wt.%, more preferably 20- 42 wt.%, and still more preferably 25-40 wt.% bio-based fly ash, based on a total dry weight of the raw materials. Technical effects of the bio-based fly ash include acting as mineralizing agent, lowering the temperature required for the formation of belite, forming additional calcium silicate hydrate and reducing heat of hydration. Technical effects further include enhanced durability, and improved resistance to sulfate attack. The bio-based fly ash can comprise aluminum oxide (AI2O3) and silicon dioxide (SiO2).

[0018] Preferably, the thermal treatment unit is a kiln, such as a cement kiln.

[0019] Preferably, the predetermined temperature in the thermal treatment unit, i.e., a processing temperature, is in a range between 1100 °C and 1350 °C, more preferably between 1 150 °C and 1300 °C, and most preferably between 1200 °C and 1300 °C. Technical effect is to provide the most desired compounds for the produced cement composition.

[0020] Preferably, the residence time is in a range between 2.5 h and 5 h, more preferably in a range between 3 h and 4.5 h, and most preferably between 3.25 h and 4.25 h. Technical effect is to provide the belite cement clinker cost efficiently.

[0021] Preferably, the raw materials to be heated in the thermal treatment unit comprise 25 to 60 wt.%, more preferably 30 to 50 wt.% calcium oxides, based on the total dry weight of the raw materials. Technical effects include efficient formation of the belite cement clinker. Technical effects further include formation of tricalcium silicate (C3S) and dicalcium silicate (C2S). Furthermore, technical effects include regulation of setting time and strength development, and hydration heat. Technical effects also include modification of physical and chemical properties of the formed belite cement, including durability and porosity.

[0022] Preferably, the raw materials to be heated in the thermal treatment unit comprise 2 to 16 wt.%, more preferably 3 to 10 wt.%, still more preferably 3 to 8 wt.%, aluminum oxide (AI2O3), based on the total dry weight of the raw materials. Technical effects include the formation of clinker phases, particularly calcium aluminates, faster setting and hardening, and higher heat of hydration. Technical effects further include improved sulfate resistance, workability, and durability, as well as improved chemical resistance.

[0023] In an embodiment, the raw materials for the belite cement clinker, to be heated in the thermal treatment unit, comprise 5 to 20 wt.%, more preferably 8 to 18 wt.% silicon dioxide (SiC ), based on the total dry weight of the raw materials. Technical effects include some desired formations of clinker phases, particularly dicalcium silicate (C2S). Technical effects further include improved strength development, hydration heat, durability, setting time and workability. Technical effects further include improved physical properties and environmental resistance.

[0024] Preferably, the raw materials for the belite cement clinker, to be heated in the thermal treatment unit, comprise 1 .5 to 10 wt.%, more preferably 2 to 6 wt.% sulfur trioxide (SO3), based on the total dry weight of the raw materials. Technical effects include the regulation of setting time and prevention of flash setting. Technical effects further include improved strength development as well as improved workability. Technical effects also include enhanced durability, moisture sensitivity, and improved resistance to sulfate attack.

[0025] Preferably, the raw materials for the belite cement clinker, to be heated in the thermal treatment unit, comprise slags from steel production up to 50 wt.%, more preferably 10-30 wt.%, based on the total dry weight of the raw materials. Technical effects include enhancement of clinker properties, improved durability, and reduced environmental impact. Technical effects further include improved hydraulic and pozzolanic properties. Technical effects further include energy savings, improved workability, mitigation of alkali-silica reaction, and adjustment of setting time. Preferably the slags from the steel production comprise, at least, CaO, SiO2, AI2O3, and MgO.

[0026] Preferably, the raw materials to be heated in the thermal treatment unit comprise aluminum sludge. Technical effects include contribution to clinker phases, improvement in hydraulic activity and influence on setting time. Technical effects also include enhancement of mechanical properties, reduced environmental impacts, and impact on durability.

[0027] Preferably, the raw materials to be heated in the thermal treatment unit comprise aluminum hydroxide AI(OH)s up to 25 wt.%, more preferably 5-15 wt.% based on a total dry weight of the raw materials. Technical effects include contribution as a source of alumina. Technical effects further include modification of clinker phases and influence on setting time, thermal decomposition, and energy efficiency. Technical effects also include improved workability, strength, and durability.

[0028] Preferably, the raw materials to be heated in the thermal treatment unit comprise up to 15 wt.%, more preferably 1 to 10 wt.%, still more preferably 2 to 6 wt.% gypsum (CaSC ), based on a total dry weight of the raw materials. Technical effects include regulation of setting time. Technical effects further include prevention of flash setting and contribution to workability. Technical effects also include influence on strength development and impact on durability as well as on heat of hydration.

[0029] The gypsum can be flue gas desulfurization gypsum. Preferably, the raw materials to be heated in the thermal treatment unit comprise flue gas desulfurization gypsum up to 15 wt.%, more preferably 1 -10 wt.% based on a total dry weight of the raw materials. Technical effects include regulation of setting time, and control of hydration heat. Technical effects further include improved strength and durability. Technical effects also include improved sulfate resistance as well as environmental benefits, and cost-effectiveness.

[0030] Preferably, the raw materials to be heated in the thermal treatment unit comprise 0 to 3 wt.%, more preferably 0.5 to 2 wt.%, calcium fluoride (CaF2), based on the total dry weight of the raw materials. Technical effects of the calcium fluoride include enhancement of clinker reactivity and modification of clinker phases. Technical effects further include improved grinding efficiency. Technical effects further include influence on setting time, hardening, and strength development. Technical effects also include enhancement of sulfate resistance, and reduction of alkali-silica reaction.

[0031] Preferably, the raw materials have a particle size wherein at least 90% of particles in the raw materials have a particle size of less than 45 pm, wherein the particle size is determined from greatest dimension of each particle before the raw materials are heated in a thermal treatment unit. Technical effect is to improve efficiency of the thermal treatment.

[0032] The raw materials for the belite cement clinker may comprise up to 100 wt.% of the above discussed components, based on the total dry weight of the belite cement clinker.

[0033] A belite cement clinker can comprise at least 20 wt.% belite (Ca2SiO4), preferably, ye’elimite (Ca4(AIO2)eSO4), and preferably, alite (CasSiOs), wherein the belite, ye’elimite, and alite form at least 40 wt.% of the belite cement clinker, preferably equal to or more than 50 wt.% of the belite cement clinker. Technical effects of this combination include that

[0034] 1 ) alite is a key for early strength and quick setting but generates more heat,

[0035] 2) belite contributes more to long-term strength and less to heat generation, enhancing durability, and

[0036] 3) ye’elimite offers rapid early strength and low hydration heat.

[0037] The belite cement clinker can comprise 1 -35 wt.%, preferably 3-25 wt.%, more preferably 5-10 wt.%, tricalcium aluminate (C3A), based on the total dry weight of the belite cement clinker. Technical effects include improved early strength development, control of setting time, and impact on durability.

[0038] The belite cement clinker can comprise 0-30 wt.%, preferably 1 -20 wt.%, more preferably 5-15 wt.% ferrite (M(FexOy)), based on the total dry weight of the belite cement clinker, where M represents any metal that forms divalent bonds. Technical effects of ferrite include a preferred effect on heat of hydration. Technical effects further include enhancement of sulfate resistance, and contribution to strength.

[0039] The belite cement clinker can further comprise 0-30 wt.%, preferably 1 -20 wt.%, more preferably 2-15 wt.% mayenite (12CaO 7Al2O3), based on the total dry weight of the belite cement clinker. Technical effects of mayenite include high early strength, improved sulfate resistance, and refractory properties. Further technical effects include improved hydration and hardening properties. Further technical effects include resistance to corrosive environments, and low pH.

[0040] The belite cement clinker can further comprise 0-5 wt.%, preferably 0.5-3 wt.%, more preferably 1 -2 wt.% anhydrite(s) (anhydrous CaSO4) based on a total dry weight of the belite cement clinker. Technical effects of anhydrites include improved setting time control. Technical effects of anhydrites further include improved strength development and durability. Technical effects also include improved heat of hydration and sulfate resistance.

[0041] Phosphorus has many technical effects for a belite cement composition. Technical effects of the phosphorus also include possibility to reuse waste material comprising phosphorus as a raw material for producing a belite cement. Thus, preferably, the belite cement clinker comprises phosphorus. The preferred amount of phosphorus in the belite cement clinker is from 0.1 wt.% to 1 .5 wt.% (by dry weight), preferably from 0.2 wt.% to 1 .0 wt.% (by dry weight).

[0042] The belite cement clinker may comprise up to 100 wt.% of the above discussed components, based on the total dry weight of the belite cement clinker.

[0043] A method for manufacturing a belite cement composition can comprise the following steps: providing a belite cement clinker comprising at least 20 wt.% belite (Ca2SiO4), wherein the belite, ye’elimite, and alite form at least 40 wt.% of the belite cement composition, and adding water, preferably wastewater, to the belite cement clinker, wherein a total amount of the belite cement clinker is at least 50 wt.% determined from a total dry weight of the belite cement composition. The method for manufacturing the belite cement composition can further comprise the following step: mixing at least 10 wt.%, and equal to or less than 50 wt.%, bio-based fly ash, and optionally, up to 20 wt.%, gypsum (CaSO4-2(H2O)) with the belite cement clinker, determined from total weight of the belite cement composition, wherein a total amount of the belite cement clinker is at least 50 wt.%, preferably equal to or more than 60 wt.%, still more preferably equal to or more than 70 wt.%, determined from a total dry weight of the belite cement composition.

[0044] The water used for producing the belite cement composition is preferably wastewater comprising at least sulfur trioxide (SOs). Technical effects of the sulfur trioxide in the wastewater include regulation of setting time and enhancement of early strength. Technical effects further include stabilization of hydration products, mitigation of shrinkage and cracking, improvement of workability, and enhanced durability.

[0045] The wastewater may further comprise sodium (Na). Technical effects include acceleration of hydration, improved workability, and controlling of setting time. Technical effects further include early strength gain, and refinement of microstructure.

[0046] The belite cement composition can comprise

[0047] 20-70 wt.%, preferably 30-60 wt.%, more preferably 40-55 wt.% belite, optionally, up to 20 wt.%, preferably 1 -15 wt.%, more preferably 2-10 wt.% ye’elimite, and optionally, up to 30 wt.%, preferably 1 -25 wt.%, more preferably 5-15 wt.% alite, wherein the belite, ye’elimite, and alite form at least 40 wt.%, preferably equal to or more than 50 wt.% of the belite cement composition (by dry weight).

[0048] Preferably, the belite cement composition comprises phosphorus. The preferred amount of phosphorus is from 0.1 wt.% to 1 .0 wt.% (by dry weight). Phosphorus has many technical effects for the belite cement composition. One technical effect is retardation of hydration. Modification of hydrate phases can affect by increasing long-term strength. Further technical effects include enhanced durability, and reduction of alkali-silica reaction. Technical effects of the phosphorus also include possibility to reuse waste material comprising phosphorus as a raw material for producing a belite cement.

[0049] A construction material, such as a concrete, can be produced by using the belite cement composition as a raw material.

[0050] Thanks to the novel method, virgin materials conventionally used in a belite cement production can be replaced with industrial side streams and / or wastes.

[0051] The belite cement clinker as well as the belite cement composition according to this specification can be good, cost efficient, and environmentally friendly product having desired properties. Further, thanks to the novel process, total environmental load including CO2 and NOx emissions can be lowered.

[0052] Brief description of the drawings

[0053] In the following, the invention will be described in more detail with reference to the appended drawings, in which:

[0054] Figs 1 -2 show some example steps for manufacturing a belite cement clinker, and

[0055] Fig. 3 shows some example steps for manufacturing a belite cement composition.

[0056] The Figures are intended to illustrate the general principles of the disclosed solution. Therefore, the illustrations in the Figures are not necessarily in scale or suggestive of precise layout of system components.

[0057] Detailed description

[0058] The solution is described in the following in more detail with reference to some embodiments, which shall not be regarded as limiting.

[0059] The following reference numbers and denotations are used in this application: 1 green liquor dregs,

[0060] 2 bio-based fly ash,

[0061] 3 water, preferably wastewater,

[0062] 4 other raw material(s),

[0063] 10 belite cement clinker,

[0064] 15 ground belite cement clinker,

[0065] 20 thermal treatment unit,

[0066] 30 first grinding and / or mixing device,

[0067] 40 second grinding and / or mixing device, and

[0068] 100 belite cement.

[0069] The embodiments and examples recited in the claims and in the specification are mutually freely combinable unless otherwise explicitly stated.

[0070] In this specification, the term “comprising” may be used as an open term, but it also comprises the closed term “consisting of.” Thus, unless otherwise indicated, the word “comprising” can be read as “comprising or consisting of”.

[0071] For the purpose of the present description and the claims, unless otherwise indicated, all ranges include any combination of the maximum and minimum points disclosed, and include any intermediate ranges therein, which may or may not be specifically enumerated herein.

[0072] Percentage values relating to an amount of a material are percentages by dry weight (wt.%) unless otherwise indicated.

[0073] In this specification, the term “GLD” refers to green liquor dregs.

[0074] The term “flue gas desulfurization gypsum” refers to an industrial by-product generated during the flue gas desulfurization. The flue gas desulfurization gypsum is typically created when sulfur dioxide is removed from the exhaust gases, for example during combustion of coal for energy production.

[0075] Alite is a form of tricalcium silicate (CasSiOs). In cement chemistry, alite can be formulated as 2CaO SiO2. Alite may comprise e.g. 3-4% of substituent oxides. Belite is based on dicalcium silicate (Ca2SiO4). In cement chemistry, belite can be formulated as 2CaO SiO2.

[0076] Ye’elimite is anhydrous calcium sulfoaluminate (Ca4(AIO2)eSO4). In cement chemistry, ye’elimite can be formulated as 4CaO3Al203-S03 or as C4A3S.

[0077] STANDARDS AND MEASUREMENTS

[0078] Unless otherwise indicated, the following standards refer to methods which are used in obtaining stated values, e.g., for representing quality of raw materials, cement composition and / or cement clinker:

[0079] Chemical Analysis:

[0080] ASTM C114, and

[0081] EN 196-2

[0082] Mineralogical Analysis:

[0083] X-Ray Diffraction (XRD) and Microscopy

[0084] Physical Properties:

[0085] ASTM C109 / C109M (compressive strength),

[0086] ASTM C151 / C151 M (volume stability),

[0087] ASTM C187 and ASTM C191 (setting time)

[0088] Fineness:

[0089] ASTM C204 (air-permeability apparatus), Blaine Air Permeability Test Durability Tests:

[0090] ASTM C1580 (determination of water-soluble sulfate in cement),

[0091] ASTM C1260 (Mortar-Bar Method), assessing the likelihood of alkali-silica reaction,

[0092] ASTM C1202 Chloride Ion Permeability Test

[0093] ASTM C114 Sulfate Content

[0094] ASTM C114 Loss on Ignition

[0095] EN 12457 Leaching Tests

[0096] RAW MATERIALS FOR A BELITE CEMENT CLINKER

[0097] The Green liquor dregs (GLD) originate from a chemical recovery cycle where cooking chemicals are regenerated from black liquor. Black liquor is a mixture of spent cooking chemicals and dissolved wood components which is resulted from delignification process where lignin is removed from wood chips. Unfortunately, GLD is still mainly landfilled. One obstacle in converting Green liquor dregs into sustainable products have been a risk of environmental pollution. Surprisingly, it is possible to use the GLD for a belite cement clinker.

[0098] Therefore, the raw materials for a belite cement clinker can comprise 10 to 90 wt.%, preferably 20 to 80 wt.%, more preferably at least 30 wt.%, and most preferably 40-60 wt.% (by dry weight) green liquor dregs (GLD). Technical effects include that by using green liquor dregs as a raw material in the belite cement production, mining and crushing of non-renewable material can be avoided. Further technical effect is to achieve significantly reduced emission of CO2.

[0099] Green liquor dregs (GLD) can be used for replacing e.g. limestone. Thus, preferably, the raw materials do not comprise limestone, or an amount of limestone is less than 10 wt.%, more preferably less than 5 wt.%, and most preferably less than 1 wt.%, determined from a total dry weight of the raw materials fed into the thermal treatment unit. Technical effect is that mining and crushing of the non-renewable limestone can be avoided.

[0100] Preferably, the green liquor dregs (GLD) comprise 20-50 wt.%, more preferably 30-50 wt.%, still more preferably 40-50 wt.%, and most preferably 45-50 wt.% Ca-based compounds, based on a total dry weight of the GLD. Technical effects include efficient formation of the belite cement clinker. Technical effects further include formation of tricalcium silicate (C3S) and dicalcium silicate (C2S). Further technical effects include regulation of setting time and strength development, and hydration heat. Technical effects also include modification of physical and chemical properties of the formed belite cement, such as durability and porosity.

[0101] Preferably, the GLD comprises 0-2 wt.%, more preferably 0.5-2 wt.%, still more preferably 1 -2 wt.%, and most preferably 1.5-2 wt.% Al-based compounds, based on the total dry weight of the GLD. Technical effects include the formation of clinker phases, particularly calcium aluminates, faster setting and hardening, and higher heat of hydration. Technical effects further include improved sulfate resistance, workability, durability, and chemical resistance. Preferably, the GLD comprises 0.1 -4 wt.%, more preferably 1 -4 wt.%, still more preferably 2-4 wt.%, and most preferably 3-4 wt.% Fe-based compounds, based on the total dry weight of the GLD. Technical effects include moderation of heat of hydration, enhancement of sulfate resistance, and contribution to strength.

[0102] Preferably, the GLD comprises 0.2-3.0 wt.%, preferably 0.2-2.0 wt.%, more preferably 0.2-1 .0 wt.%, and most preferably 0.2-0.5 wt.%, S-based compounds, based on the total dry weight of the GLD. Technical effects include regulation of setting time and prevention of flash setting. Technical effects further include improved strength development as well as improvement of workability. Technical effects also include enhanced durability, moisture sensitivity, and improved resistance to sulfate attack.

[0103] Preferably, the GLD comprises 0.1 -1 wt.%, preferably 0.2-1 wt.%, more preferably 0.3-1 wt.%, and most preferably 0.5-1 wt.% Si-based compounds, based on the total dry weight of the GLD. Technical effects include the improved formation of clinker phases, particularly dicalcium silicate (C2S). Technical effects further include improved strength development, hydration heat, durability, and setting time. Technical effects further include improved workability, physical properties, and environmental resistance.

[0104] The raw materials for the belite cement clinker can comprise a fly ash, preferably a bio-based fly ash.

[0105] The raw materials can comprise up 50 wt.%, preferably 10 to 45 wt.% (by dry weight), more preferably 20 to 40 wt.%, and most preferably 25-35 wt.% (by dry weight) bio-based fly ash. Technical effects include replacing virgin raw materials with suitable waste material(s), hence, improving environmental friendliness of the obtained product. Further technical effect is that bio-based fly ash is typically a source of silica and alumina. Technical effects further include a potential to lower clinkering temperature and provide improved pozzolanic properties. Technical effects further include improved sulfate resistance, and reduced alkali-silica reaction.

[0106] The bio-based fly ash can be obtainable from a combustion of bio-based material. Preferably, the bio-based fly ash is obtained from a combustion of forest industry material. The bio-based fly ash can be obtained from power plant using forest industry material.

[0107] Preferably, the bio-based fly ash is formed by combusting material comprising or consisting of wood based material. Thus, preferably, the bio-based fly ash is a wood-based fly ash. One technical effect is that this kind of bio-based fly ash can supply silica and alumina. Further technical effects include potential to lower clinkering temperature, provide additional pozzolanic properties, improve sulfate resistance, and reduce alkali-silica reaction.

[0108] Preferably, the bio-based fly ash comprises 2-19 wt.%, more preferably 5-19 wt.%, still more preferably 10-19 wt.%, and most preferably 15-19 wt.%, Si- based compounds, such as silicon dioxide (SiO2), based on the total dry weight of the bio-based fly ash. Technical effects include the improved formation of clinker phases, particularly dicalcium silicate (C2S). Technical effects further include improved strength development and improved hydration heat, durability, setting time and workability. Technical effects also include improved physical properties, and environmental resistance.

[0109] Preferably, the bio-based fly ash comprises 2-21 wt.%, more preferably 5-21 wt.%, still more preferably 10-21 wt.%, and most preferably 15-21 wt.% Al- based compounds, such as aluminum oxide (AI2O3), based on the total dry weight of the bio-based fly ash. Technical effects include improved formation of clinker phases, particularly calcium aluminates. Technical effects further include faster setting and hardening, and higher heat of hydration. Technical effects further include improved sulfate resistance, workability, durability, and chemical resistance.

[0110] The bio-based fly ash can comprise calcium. Calcium may be in a form of any calcium compound. Preferably, the bio-based fly ash comprises 5-57 wt.%, more preferably 20-57 wt.%, still more preferably 30-57 wt.%, and most preferably 40-57 wt.%, Ca-based compounds, based on the total dry weight of the bio-based fly ash. Technical effects include efficient formation of the belite cement clinker. Technical effects further include formation of tricalcium silicate (C3S) and dicalcium silicate (C2S). Further technical effects include regulation of setting time and strength development, and hydration heat. Technical effects also include modification of physical and chemical properties of the formed cement, such as durability and porosity.

[0111] Preferably, the bio-based fly ash comprises 1 -20 wt.%, more preferably 5-20 wt.%, still more preferably 10-20 wt.%, and most preferably 15-20 wt.% Fe- based compounds, based on the total dry weight of the bio-based fly ash. Technical effects include moderation of heat of hydration, enhancement of sulfate resistance, and contribution to strength.

[0112] Preferably, the bio-based fly ash comprises 0.1 -5 wt.%, preferably 1 -5 wt.%, more preferably 2-5 wt.%, and most preferably 3-5 wt.% S-based compounds, based on the total dry weight of the bio-based fly ash. Technical effects include the regulation of setting time and prevention of flash setting. Technical effects further include improved strength development as well as improvement of workability. Technical effects also include enhanced durability, moisture sensitivity, and improved resistance to sulfate attack.

[0113] Moisture content of the bio-based fly ash can be less than 40 %, such as 0 - 40 % (w / w) based on a total weight of the bio-based fly ash.

[0114] The raw materials of the belite cement clinker can be ground before the mixture is fed into the thermal treatment unit in order to improve efficiency of the thermal treatment. Preferably, at least 90% of particles in the raw materials to be fed into the thermal treatment unit have a particle size of less than 45 pm, wherein the particle size is determined from the greatest dimension of each particle.

[0115] In an advantageous embodiment, the raw materials for the belite cement clinker comprises at least 40 wt.% green liquor dregs and at least 20 wt.% biobased fly ash. Technical effects include increased belite formation. Technical effects further include formation of aluminates and ferrites. Technical effects further include lowered clinkering temperature, improving the product efficiency. Technical effects also include enhanced early strength, improved particle packing, improved durability, and mitigation of alkali-silica reaction.

[0116] A mixture can be formed from the raw materials before the raw materials are heated in the thermal treatment unit. Preferably, the raw materials (for the belite cement clinker, to be heated in the thermal treatment unit) comprise 25 to 60 wt.%, more preferably 30 to 50 wt.% calcium oxides, based on the total dry weight of the raw materials. Technical effects include forming additional calcium silicate phases and especially belite. Technical effects also include alteration of aluminate and ferrite phases. Technical effects further include improved energy efficiency as well as improved early strength.

[0117] Preferably, the raw materials (for the belite cement clinker, to be heated in the thermal treatment unit) comprise 2 to 16 wt.%, more preferably 3 to 8 wt.% aluminum oxide (AI2O3), based on the total dry weight of the raw materials. Technical effects include contribution to formation of calcium aluminate phases. Further technical effects include effect on stability and formation rate of belite. Further technical effects include improved early strength, setting time, heat of hydration, sulfate resistance, and reduced alkali-silica reaction.

[0118] Preferably, the raw materials to be heated in the thermal treatment unit comprise 5 to 20 wt.%, more preferably 8 to 18 wt.% silicon dioxide (SiC ), based on the total dry weight of the raw materials. Technical effects include enhanced belite formation and promoted formation of other silicate phases. Technical effects further include enhanced late strength development, lower porosity, and denser cement. Particularly advantageous technical effects are an improved durability and improved resistance to environmental attacks.

[0119] Preferably, the raw materials to be heated in the thermal treatment unit comprise 1.5 to 10 wt.%, more preferably 2 to 5 wt.% sulfur trioxide (SO3), based on the total dry weight of the raw materials. Technical effects include an extended setting time, improved formation of sulfate containing phases, improved workability and consistency, enhanced durability and reduced alkalisilica reaction, and hydration heat.

[0120] Preferably, the raw materials to be heated in the thermal treatment unit comprise slags from steel production 0-50 wt.%, more preferably 5-30 wt.%, based on the total dry weight of the raw materials. The addition of slags can cause higher need of grinding energy, improved workability, and increased water demand. Technical effects include improved formation of belite and other silicate phases, slower initial set and prolonged strength development and setting time. Further technical effects include improved durability and resistance to chemical attack. Preferably, the slags from steel production comprise CaO, SiO2, AI2O3, and MgO.

[0121] Preferably, the raw materials to be heated in the thermal treatment unit comprise flue gas desulfurization gypsum up to 15 wt.%, more preferably 1 -10 wt.% based on the total dry weight of the raw materials. Technical effect is extended setting time, improved formation of sulfate containing phases, improved workability and consistency, enhanced durability and reduced alkalisilica reaction, and hydration heat.

[0122] Preferably, the raw materials to be heated in the thermal treatment unit comprise aluminum sludge. Technical effects include formation of calcium aluminate phases and belite, lower clinkering temperature, enhanced hydration, enhanced durability, improved resistance to chemical attack, and lower hydration heat.

[0123] Preferably, the raw materials to be heated in the thermal treatment unit comprise aluminum hydroxide AI(OH)s up to 25 wt.%, more preferably 5-20 wt.%, based on the total dry weight of the raw materials. Technical effects include forming aluminate phases, promoted formation of aluminate compounds, lower clinkering temperature, particle size distribution, accelerated hydration, accelerated setting time, enhanced durability, and enhanced resistance to thermal and mechanical stresses.

[0124] Preferably, the raw materials to be heated in the thermal treatment unit comprise up to 15 wt.%, preferably 1 to 4 wt.%, gypsum (CaSC ), based on a total dry weight of the raw materials. Technical effects include improved controllability of the hydration of calcium aluminate phases, enhanced reactivity of belite, extended setting time, improved workability, lower hydration heat, lower early and higher final strength, enhanced durability, and improved volume stability.

[0125] Preferably, the raw materials to be heated in the thermal treatment unit comprise up to 3 wt.%, preferably 0.5 to 2 wt.% calcium fluoride (CaF2), based on the total dry weight of the raw materials. Technical effects include lower clinkering temperature, faster clinker formation, improved stabilization of belite phase, improved formation of dicalcium silicate, improved grindability, accelerated setting time, enhanced early strength and improved sulfate resistance.

[0126] Advantageously, the raw materials for the belite cement clinker comprises

[0127] 25 to 60 wt.%, preferably 30 to 50 wt.%, more preferably 37 to 50 wt.% (by dry weight) calcium oxides,

[0128] 2 to 16 wt.%, preferably 4 to 8 wt.% (by dry weight) aluminum oxide (AI2O3),

[0129] 1 to 20 wt.%, preferably 5 to 18 wt.%, more preferably 8 to 18 wt.% silicon dioxide (SiC>2), and

[0130] 1 .5 to 10 wt.%, preferably 2 to 5 wt.% sulfur trioxide (SO3), all percentages being based on the total dry weight of the raw materials. Technical effects of this combination include that the raw materials are tailored to produce a high-quality belite cement with specific properties including improved durability, controlled setting time, and excellent long-term strength development.

[0131] BELITE CEMENT CLINKER

[0132] The cement clinker according to this specification is a belite cement clinker comprising belite.

[0133] The belite cement clinker can comprise at least 20 wt.%, such as 20-70 wt.% belite, more preferably at least 30 wt.%, such as 30-40 wt.% and most preferably 40-60 wt.% belite (Ca2SiO4). Such cement clinker, compared to typical Portland cement dominated by alite, gives technical effects including slower early strength but continued strength gain, increased durability, and reduced alkali-sil ica reaction.

[0134] The belite cement clinker can comprise ye’elimite (Ca4(AIO2)eSO4). The belite cement clinker can comprise 0-15 wt.%, preferably 5-15 wt.%, more preferably 10-15 wt.%, ye’elimite, based on the total dry weight of the belite cement clinker. Technical effects of incorporating higher amounts ye’elimite in the belite cement clinker include rapid early strength development, enhanced durability against sulfate attack, and environmental advantages e.g. due to lower production temperatures.

[0135] The belite cement clinker can comprise alite (CasSiOs). The belite cement clinker can comprise 0-40 wt.%, preferably 20-40 wt.%, more preferably 30-40 wt.% alite, based on the total dry weight of the belite cement clinker. Technical effect is that the alite in the belite cement clinker significantly enhances the early performance characteristics of the belite cement, particularly in terms of strength development and setting times.

[0136] The belite, ye’elimite, and alite form at least 40 wt.% of the belite cement clinker (by dry weight). The belite, ye’elimite, and alite can form 40-100 wt.%, preferably 60-100 wt.%, more preferably 80-100 wt.% of the belite cement clinker, based on the total dry weight of the belite cement clinker. Technical effects include that belite cement clinker comprising alite, belite, and ye’elimite offers a robust solution combining rapid early strength, long-term durability, and enhanced environmental resistance.

[0137] The belite cement clinker can comprise 0-30 wt.%, preferably 10-30 wt.%, more preferably 20-30 wt.% aluminate (AIOs), based on the total dry weight of the belite cement clinker. Technical effect is that the inclusion of aluminate in the belite cement clinker enhances early strength and setting characteristics while also contributing to durability in sulfate-rich environments.

[0138] The belite cement clinker can comprise 0-20 wt.%, preferably 5-20 wt.%, more preferably 10-20 wt.%, ferrite (M(FexOy)), based on a total dry weight of the belite cement clinker, where M represents any metal that forms divalent bonds. Technical effects include that ferrite in belite cement clinker contributes to the color, hydration characteristics, strength development, and durability of the belite cement.

[0139] The belite cement clinker can comprise 0-20 wt.%, preferably 5-20 wt.%, more preferably 10-20 wt.%, mayenite (12CaO-7Al2Os), based on the total dry weight of the belite cement clinker. Technical effects of incorporating mayenite into belite cement clinker include enhanced early strength properties, improved durability, and typically reduced environmental impact. The belite cement clinker can comprise 0-10 wt.%, preferably 2-7 wt.%, more preferably 3-5 wt.%, acid anhydride(s) based on the total dry weight of the belite cement clinker. The most relevant anhydride is sulfur trioxide (SOs), which can be present in the form of sulfur anhydride (sulfur trioxide). Sulfur anhydride in the clinker can affect the sulfur content of the belite cement. High levels of sulfur anhydride can lead to the formation of calcium sulfoaluminate and other sulfate-containing phases during clinker formation and hydration. Excessive amounts of sulfur anhydrides can cause expansion issues in the belite cement due to the formation of secondary ettringite during the later stages of hydration, which can lead to cracking and reduced durability of the belite cement.

[0140] The belite cement clinker can comprise 1 -30 wt.%, preferably 10-30 wt.%, more preferably 20-30 wt.% tricalcium aluminate (3CaO Al2Os), based on the total dry weight of the belite cement clinker. The tricalcium aluminate can also be formulated as CasA^Oe. Technical effect is that said addition significantly enhances the early performance characteristics of the belite cement, particularly in terms of strength development and setting times.

[0141] The belite cement clinker can comprise 0-20 wt.%, preferably 2-15 wt.%, more preferably 5-15 wt.%, tetra-calcium aluminoferrite (4CaO ■ Al2OsFe2O3, also formulated as C4AF), based on the total dry weight of the belite cement clinker. Technical effects include that C4AF in the belite cement clinker adds value in terms of color. Technical effects further include moderate contribution to strength, enhanced durability against sulfate attack and chloride penetration, and reduced heat of hydration.

[0142] Advantageously, the belite cement clinker comprises phosphorus (P). Amount of phosphorus is preferably 0.1 -1 .5 wt.%, more preferably 0.2-1 .0 wt.%, more preferably 0.2-0.9 wt.%, and most preferably 0.3-0.8 wt.%, determined from the total dry weight of the belite cement clinker. One technical effect is to reuse waste material comprising phosphorus as a raw material for producing a belite cement. Surprising technical effects include retardation of hydration, wherein modification of hydrate phases can affect increasing long-term strength and enhance durability. Furthermore, thanks to the phosphorus, and particularly when amount of phosphorus is 0.1 -1 .0 wt.%, more preferably 0.2-0.8%, alkalisilica reaction can be decreased. The cement clinker can comprise some of the above discussed materials, selected according to a need.

[0143] The cement clinker can comprise up to 100 wt.% the above discussed materials, i.e., the cement clinker can consist of the above discussed materials.

[0144] Preferably, the cement clinker comprises at least the belite and the phosphorus, wherein the belite, ye’elimite, and alite form at least 40 wt.% of the belite cement clinker (by dry weight).

[0145] BELITE CEMENT COMPOSITION

[0146] The belite cement composition can comprise

[0147] - the belite cement clinker according to this specification, preferably ground belite cement clinker wherein at least 90% of particles in the raw materials have a particle size of less than 45 pm, wherein the particle size is determined from greatest dimension of each particle,

[0148] - optionally, bio-based fly ash, and

[0149] - optionally, gypsum,

[0150] Technical effect is to improve environmental friendliness of the product. Further technical effect is to decrease manufacturing costs.

[0151] The belite cement clinker in the belite cement composition can comprise the previously discussed proportion of compounds.

[0152] For obtaining the advantages, a total amount of the belite cement clinker according to this description, determined from a total dry weight of the belite cement composition, is preferably at least 50 wt.%, more preferably equal to or more than 60 wt.%, and most preferably equal to or more than 70 wt.%.

[0153] The belite cement composition can comprise e.g. at least 50 wt.% a belite cement clinker comprising 1 -35 wt.%, preferably 3-25 wt.%, more preferably 5-10 wt.%, tricalcium aluminate (C3A), based on the total dry weight of the belite cement clinker. Technical effects include improved durability.

[0154] Advantageously, the belite cement composition comprises 20-70 wt.%, preferably belite, 0-20 wt.%, preferably 1 -15 wt.% ye’elimite, and 0-30 wt.%, preferably 1 -25 wt.% alite, determined from a total dry weight of the belite cement composition, wherein the belite, ye’elimite, and alite form at least 40 wt.% (by dry weight) of the belite cement composition, and wherein the belite cement composition further comprises phosphorus, optionally, an amount of phosphorus is 0.1 -1.0 wt.%, preferably 0.2-0.7%, determined from the total dry weight of the belite cement composition.

[0155] Preferably, the belite cement composition comprises Ca-, AI-, Si- and S- based compounds. Technical effect is to increase hardening in the product.

[0156] The belite cement composition can comprise phosphorus (P). The amount of phosphorus is preferably 0.1 -1 .0 wt.%, more preferably 0.2-0.9 wt.%, still more preferably 0.3-0.8 wt.%, and most preferably 0.3-0.7 wt.%, determined from the total dry weight of the belite cement composition. Technical effects include reusing waste material comprising phosphorus as a raw material for producing the belite cement composition. Another technical effect is retardation of hydration and, further, modification of hydrate phases can increase long-term strength. Technical effects further include enhanced durability, and reduced alkali-silica reaction.

[0157] In an embodiment, the belite cement composition may comprise cadmium (Cd). Technical effect is to reuse waste material comprising cadmium as a raw material for producing a belite cement composition. In an embodiment, the belite cement composition may comprise vanadium (V). Technical effect is to reuse waste material comprising vanadium as a raw material for producing a belite cement composition.

[0158] The belite cement composition can comprise compounds from wastewater, such as compounds from mine water concentrate. The wastewater, such as the mine water concentrate, preferably comprises:

[0159] - 0.1 -1.0 ppm S,

[0160] - 0.01 -0.1 ppm Na, and

[0161] - 0.01 -0.1 ppm K. One technical effect is to use wastewater for a novel product and decrease environmental effects of mine water. Further technical effect is to improve properties of the produced belite cement composition. Still further technical effect is to replace at least part of gypsum (conventionally used in a belite cement) with wastewater, hence at least reducing a need of gypsum in the belite cement composition.

[0162] Preferably, the belite cement composition comprises

[0163] - 30-60 wt.% Ca-based compounds,

[0164] - 2-20 wt.% Al-based compounds,

[0165] - 2-10 wt.% S-based compounds,

[0166] - 5-25 wt.% Si-based compounds,

[0167] - 0-30 wt.%, preferably 5-20 wt.% Fe-based compounds,

[0168] - 0-5 wt.%, preferably 1 -4 wt.% Na-based compounds,

[0169] - 0-5 wt.%, preferably 1 -4 wt.% K-based compounds, and

[0170] - 1 -10 wt.% Mg-based compounds, wherein all percentages are by dry weight and a total amount of said compounds is up to 100 wt.%, determined from the total dry weight of the belite cement composition. Technical effects include that such belite cement composition is designed to provide a balance between early and long-term strength development. The mix of sulfate, aluminate, and silicate compounds enhances the resistance to chemical attacks and environmental exposure. The presence of fluxes like sodium and potassium, along with iron, can reduce the energy required for clinker formation.

[0171] METHOD FOR MANUFACTURING A BELITE CEMENT CLINKER

[0172] The method for manufacturing a belite cement clinker comprises a step of treating raw materials in a thermal treatment unit, such as in a kiln. Thus, the method can comprise a step of feeding raw materials to the thermal treatment unit.

[0173] Thus, a method for manufacturing a belite cement clinker can comprise: providing raw materials comprising

[0174] 10 to 90 wt.%, preferably 20 to 80 wt.% (by dry weight) green liquor dregs (GLD), and 0 to 50 wt.%, preferably 10 to 40 wt.% (by dry weight) bio-based fly ash, heating the raw materials in a thermal treatment unit by using a process temperature and a residence time, thereby forming the belite cement clinker.

[0175] The raw materials can further comprise SiO2-, F-, Al- and / or S- containing industrial side stream(s) and / or waste material(s), e.g., as discussed in this specification.

[0176] A feeding device can be used for supplying the raw materials into the thermal treatment unit.

[0177] Before the raw materials are fed into the thermal treatment unit, the raw materials can be pre-treated.

[0178] The pre-treatment(s) can comprise at least one of grinding, screening, preheating, or mixing.

[0179] A mixing and / or a grinding device can be used for mixing and / or grinding the raw materials.

[0180] Thus, the method can comprise a step of grinding the raw materials before heating the raw materials in the thermal treatment unit. Alternatively, or in addition, the method can comprise a step of mixing the raw materials before heating the raw materials in the thermal treatment unit. The technical effect is to improve efficiency of the thermal treatment.

[0181] Thus, the raw materials, or at least part of the raw materials, can be treated for decreasing particle size of said raw material(s). In an embodiment, the raw materials are treated so that at least 90% of particles in the raw materials have a particle size of less than 45 pm, wherein the particle size is determined from greatest dimension of each particle. Technical effect is to improve efficiency of the heating step. Preferably, the raw materials are at least mixed with each other. The raw materials can be fed as a mixture to the thermal treatment unit with or without a preheating system.

[0182] Thus, the method can comprise a step of pre-heating the raw materials before heating the raw materials in the thermal treatment unit. The technical effect is to improve efficiency of the thermal treatment.

[0183] The thermal treatment unit can be selected from group consisting of a lime kiln, lime sludge reburning kiln, cement kiln, chamber oven, chamber furnace, heat treatment oven and their combinations. Preferably, a cement kiln, more preferably a rotary kiln, is used as the thermal treatment unit.

[0184] The thermal treatment unit can be used to provide a sufficiently high processing temperature and residence time for obtaining a belite cement clinker. Preferably, the raw materials are moved during the treatment in the thermal treatment unit.

[0185] The process temperature is preferably lower that in production of Portland cement. The process temperature of Portland cement may be approximately 1450 °C

[0186] The raw materials can be treated at a process temperature of 1100-1350 °C, more preferably between 1150 °C and 1300 °C, and most preferably between 1200 °C and 1300 °C. Technical effect is to produce the belite cement clinker cost efficiently. Further technical effect is to improve environmental friendliness of the process by using a substantially low temperature for obtaining the belite cement clinker. Further technical effect is to avoid melting of the raw materials.

[0187] The raw materials can be treated at a process temperature with a residence time of 2.5 - 5 hours, preferably 3-4.5 hours, more preferably 3.2-4.2 hours. Technical effect is to produce the belite cement clinker cost efficiently.

[0188] METHOD FOR MANUFACTURING A BELITE CEMENT COMPOSITION

[0189] A method for manufacturing a belite cement composition can comprise steps of - providing a belite cement clinker, preferably ground belite cement clinker, wherein at least 90% of particles have a particle size of less than 45 pm, wherein the particle size is determined from greatest dimension of each particle,

[0190] - mixing water, preferably wastewater, with the belite cement clinker, wherein amount of the belite cement clinker is at least 50 wt.% determined from a total dry weight of the belite cement composition.

[0191] Thus, the method for manufacturing the belite cement composition can comprise a step of mixing wastewater with the ground belite cement clinker. Technical effects include improving properties of the obtained belite cement composition. Further technical effects include improving environmental friendliness of the method as wastewater can be used as a raw material for the belite cement composition.

[0192] The method for manufacturing the belite cement composition can further comprise a step of mixing gypsum, such as desulphurization gypsum with the belite cement clinker.

[0193] The method for manufacturing the belite cement composition can further comprise a step of grinding and / or sieving the obtained belite cement composition.

[0194] EXPERIMENTAL TESTS

[0195] Example 1

[0196] Green liquor dregs and bio-based fly ash were mixed and added into a kiln. The process temperature and residence time were according to this specification. During the processing, fly ash and green liquor dregs were activated. The obtained belite cement clinker was suitable as a main raw material for a belite cement composition.

[0197] Example 2

[0198] Different raw material mixtures were produced, including a test point comprising - 50 wt.% green liquor dregs,

[0199] - 25 wt.% bio-based fly ash,

[0200] - 10 wt.% lime kiln dust from GLD production,

[0201] - 4 wt.% Al-sludge,

[0202] - 6 wt.% silica powder,

[0203] - 4 wt.% fosfogypsum, and

[0204] - 1 wt.% CaF2.

[0205] The mixture of this test point was ground so that 90% of particles in the mixture had a particle size of less than 45 pm.

[0206] The mixture was treated in a rotary kiln having a processing temperature of 1200 °C with a residence time of 4h.

[0207] After the treatment, a belite cement clinker was formed. The formed cement clinker had desired properties.

[0208] Example 3

[0209] Several test points comprising the following raw materials were prepared:

[0210] - GLD from 15 to 35 wt.%,

[0211] - fly ash 20-30 wt.%,

[0212] - slags 25-45 wt.%, and

[0213] - flue gas desulfurization gypsum from 10 to 17 wt.%.

[0214] Some tests points further comprised aluminum hydroxide.

[0215] For these test points, the process parameters were as follows:

[0216] For some test points temperature exceeded 1300 °C. It was noted that the temperatures of less than 1100 °C and more than 1350 °C caused problems to the process and / or the quality of the produced cement clinker. For all test points, an amount of belite in the obtained cement clinker was more than 20 wt.% (by dry weight).

[0217] Some example clinker compositions were as follows (by dry weight) tetra-calcium aluminoferrite

[0218] 2C4A3$ Ye’elimite

[0219] 3C2S dicalcium silicate

[0220] 4C$ Anhydrite

[0221] 5Cm "Alkalinity index” = (CaO - 0,7TiO2) / (1 ,87SiO2+0,73(AI2O3-

[0222] 0,64Fe2Os)+1 ,4Fe20s)

[0223] 6P ’’Alumina-sulfur ratio” = (AI2Os - 0,64 Fe2Os) / SO37N ’’Alumina-silica ratio” = Al2Os / SiO2

[0224] 8C / S ’’Calcium - silica ratio” = CaO / SiO2

[0225] Cement compositions according to this specification were produced.

[0226] For example, a belite cement composition comprising

[0227] - 50 wt.% cement clinker (according to this specification), and

[0228] - 47.5 wt.% bio-based fly ash, was formed.

[0229] The formed composition was ground so that 90% of particles in the mixture had a particle size of less than 45 pm.

[0230] The belite cement compositions had desired properties including suitable strength properties.

[0231] Concrete compositions comprising

[0232] - 100 parts of the belite cement composition according to this specification, and

[0233] - 36-60 parts mine water concentrate were formed.

[0234] The concrete compositions had desired properties including suitable strength properties.

[0235] The invention has been described with the aid of illustrations and examples.

[0236] The invention may be modified within the scope of the appended claims.

Claims

Claims:1 . A method for manufacturing a belite cement clinker, the method comprising providing raw materials comprising10 to 90 wt.%, preferably 20 to 80 wt.% green liquor dregs (GLD), based on a total dry weight of the raw materials, and0 to 50 wt.%, preferably 10 to 45 wt.% bio-based fly ash, based on the total dry weight of the raw materials, heating a mixture comprising the raw materials in a thermal treatment unit by using a process temperature and a residence time, thereby forming a belite cement clinker.

2. The method according to claim 1 , wherein the raw materials comprise phosphorus, preferably 0.1-1 .0 wt.% based on the total dry weight of the raw materials.

3. The method according claim 1 or 2, wherein the raw materials comprise25 to 60 wt.%, preferably 30 to 50 wt.% calcium oxides,2 to 16 wt.%, preferably 3 to 8 wt.% aluminum oxide (AI2O3),5 to 20 wt.%, preferably 8 to 18 wt.% silicon dioxide (SiC ) and1 .5 to 10 wt.%, preferably 2 to 6 wt.% sulfur trioxide (SO3), based on the total dry weight of the raw materials.

4. The method according claim 1 or 2 or 3, wherein the raw materials comprise up to 15 wt.%, preferably 1 to 10 wt.%, more preferably 2 to 6 wt.% gypsum (CaSC ), and / or up to 3 wt.%, preferably 0.5 to 2 wt.% calcium fluoride (CaF2), based on the total dry weight of the raw materials.

5. The method according to any of the preceding claims, wherein the raw materials comprise at least one of: slags from steel production up to 50 wt.%, flue gas desulfurization gypsum up to 15 wt.%, and aluminum hydroxide AI(OH)s up to 25 wt.%, based on the total dry weight of the raw materials.

6. The method according to any of the preceding claims, wherein at least 90% of particles in the raw materials have a particle size of less than 45 pm, wherein the particle size is determined from greatest dimension of each particle before the raw materials are heated in a thermal treatment unit.

7. The method according to any of the preceding claims, wherein the process temperature is in a range between 1100 °C and 1350 °C, preferably between 1200 °C and 1300 °C, and / or the residence time is in a range between 2.5 h and 5 h, preferably in a range between 3 h and 4.5 h.

8. The method according to any of the preceding claims, wherein the raw materials comprise 30-80 wt.%, preferably 40-70 wt.% green liquor dregs (GLD), based on the total dry weight of the raw materials.

9. The method according to any of the preceding claims, wherein the bio-based fly ash comprises aluminum oxide (AI2O3) and silicon dioxide (SiC ), and the raw materials comprise 15-50 wt.%, preferably 20-40 wt.% bio-based fly ash, based on the total dry weight of the raw materials.

10. The method according to any of the preceding claims, wherein the raw materials comprise aluminum sludge.11 . A belite cement clinker obtainable according to any of the preceding claims 1-10.

12. A belite cement clinker comprising at least 20 wt.% belite (Ca2SiO4), determined from a total dry weight of the belite cement clinker, optionally, ye’elimite (Ca4(AIO2)eSO4), optionally, alite (CasSiOs), and optionally, aluminate (AIO3), wherein the belite, ye’elimite, and alite form at least 40 wt.% of the belite cement clinker, determined from the total dry weight of the belite cement clinker, and wherein the belite cement clinker further comprises phosphorus,optionally, an amount of phosphorus is 0.1-1 .0 wt.%, more preferably 0.2-0.7 wt.%, determined from the total dry weight of the belite cement clinker.

13. The belite cement clinker according to claim 12, wherein the belite cement clinker comprises at least one of: ferrite (M(FexOy)), where M represents any metal that forms divalent bonds, mayenite (12CaO-7Al2Os), and sulfur anhydride.

14. A method for manufacturing a belite cement composition, the method comprising providing the belite cement clinker according to claim 11 or 12 or 13, or providing the belite cement clinker obtainable according to any of the preceding claims 1 to 10, adding water, preferably wastewater, to the belite cement clinker, wherein amount of the belite cement clinker is at least 50 wt.% determined from a total dry weight of the belite cement composition.

15. The method according to claim 14, wherein the method further comprises: adding10-50 wt.% bio-based fly ash, and0-20 wt.%, gypsum (CaSO4‘2(H2O)) to the belite cement clinker, determined from the total dry weight of the belite cement composition.

16. The method according to claim 14 or 15, wherein the water comprises sulfur trioxide (SOs), and optionally, sodium (Na).

17. A belite cement composition obtainable according to any of the preceding claims 14-16.

18. A belite cement composition comprising20-70 wt.%, preferably 30-60 wt.%, belite,0-20 wt.%, preferably 1 -15 wt.%, ye’elimite, and0-30 wt.%, preferably 1 -25 wt.% alite,determined from a total dry weight of the belite cement composition, wherein the belite, ye’elimite, and alite form at least 40 wt.% (by dry weight) of the belite cement composition, and wherein the belite cement composition further comprises phosphorus, optionally, an amount of phosphorus is 0.1 -1.0 wt.%, preferably 0.2-0.7%, determined from the total dry weight of the belite cement composition.

19. A construction material, such as a concrete, comprising the belite cement composition according to claim 17 or 18.

20. A use of green liquor dregs in a production of a belite cement composition.

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