PROCESS FOR PREPARING HYDRAULIC LIME

Abstract

PROCESS FOR PREPARING HYDRAULIC LIME The present invention relates to a process for preparing hydraulic lime by flash calcination of a clay-silico-calcareous composition, comprising a clay-silico-calcareous filler, said flash calcination step being carried out at a temperature of from 720°C to 900°C. Figure for abstract: none

Description

Title of the invention: PROCESS FOR THE PREPARATION OF HYDRAULIC LIME

[0001] The present invention relates to a process for preparing hydraulic lime, in particular natural hydraulic lime.

[0002] The construction sector represents a significant part of France's economic activity. The significant role of this sector and the construction / renovation of the building stock leads to a continuous and significant consumption of natural resources, a significant release of CO2 and a significant consumption of energy. The public authorities' awareness of the need to reduce greenhouse gas emissions tends to improve the environmental and energy performance of the construction sector, both in terms of materials and the design of structures. In the construction sector, the increase in the price of raw materials, the depletion of natural resources and the administrative difficulties of opening new quarry sites tend to move towards alternative resources such as recycled aggregates or industrial co-products.In the field of industrial co-products, quarry washing fines can be considered as a resource with high potential for recovery in the field of eco-materials, due to their large volumes and their clayey nature.

[0003] Most of the aggregates used in the construction industry come from alluvial or massive quarries. To meet the quality and performance criteria of the materials and products used (concrete, treated gravel, etc.), the aggregates must only contain a small quantity of clayey fines so as not to cause adhesion problems, particularly between the cement matrix and the aggregates for concrete. Therefore, washing units clean the aggregates and remove the fines.

[0004] For alluvial quarries, the washing fines are discharged into old excavations as soon as they leave the facilities. The exploitation of a massive quarry requires mining and reworking of the natural terrain. The production of aggregates leads to the production of by-products which can be unexploited and stored like quarry washing fines.

[0005] However, these fines require significant storage capacities and can be a disadvantage in terms of the exploitation of the deposit. Indeed, the aggregate washing fines, at the outlet of the process, have a more or less significant concentration in the water (150 g / l to 750 g / l). The washing water cannot be discharged into the water table due to these significant concentrations. Consequently, settling basins make it possible to store this sludge in order to separate the water from the fines. washing. Currently, washing fines are not highly valued. The increase in aggregate production is generating significant volumes of these fines.

[0006] It is therefore necessary today, in order to preserve natural material resources, to find ways of exploiting these fine clay-silico-limestones.

[0007] The present invention aims to reduce the storage volumes of the washing sludge fines mentioned above.

[0008] The aim of the invention is therefore to propose a process allowing the recycling of quarry waste, in particular wash water containing fine clay-silico-limestone.

[0009] To this end, the invention relates to a process for preparing hydraulic lime, in particular natural hydraulic lime, by flash calcination of a clay-silico-calcareous composition, comprising a clay-silico-calcareous filler, said flash calcination step being carried out at a temperature of from 720°C to 900°C.

[0010] The method of the invention is therefore based on a heat treatment of a clay-silico-limestone composition, namely a composition comprising in particular clay, silica and limestone, as explained below.

[0011] This process differs from current processes that transform limestone into hydraulic lime, generally between 900°C and 1,200°C in vertical kilns. The residence time of the limestone in these kilns is 24 hours. And the size of the stones for vertical kilns is usually 20 / 150 mm. The fine fraction (0 / 20) is often not highly valued.

[0012] Thus, the present invention not only allows thermal transformation at a lower set temperature and with a very short residence time but above all the use of very fine materials, all allowing partial decarbonation and a significant CO2 gain.

[0013] The method of the invention is advantageous in particular in that it makes it possible to obtain a gain in CO2 on the calcined product, and this in particular thanks to the implementation of the flash calcination step. The use of a flash calciner makes it possible to significantly reduce the energy required for calcination and the material obtained does not require any grinding after flash calcination.

[0014] By "hydraulic lime" or HL (for "hydraulic lime" in English), we mean a lime which has a hydraulic setting, namely a setting under the action of water.

[0015] By "natural hydraulic lime" or NHL (for "natural hydraulic lime" in English), we mean a lime which has an aerial setting and a hydraulic setting, namely a setting under the action of carbon dioxide in the air and a setting under the action of water.

[0016] According to the NF EN 459-1 standard relating to construction lime, a natural hydraulic lime is a lime produced by calcining more or less clayey or siliceous limestone with reduction to powder by slaking, with or without grinding. They all have the property of setting and hardening in the presence of water. The carbon dioxide present in the air also contributes to the hardening process. NHLs do not contain any additives.

[0017] Thus, the present invention relates to a process which surprisingly allows, under specific conditions, the obtaining of a hydraulic lime, in particular a natural hydraulic lime, which corresponds well to the standard. It is the conditions of the heat treatment by flash calcination as mentioned above which allow a suitable product to be obtained.

[0018] The specific heat treatment implemented according to the method of the invention is a calcination with a very short treatment time, namely a flash calcination. Flash calcination technology is a technology well known to those skilled in the art, which makes it possible to calcine fine particles in hot gases for a very short residence time, more particularly of the order of a second.

[0019] As indicated above, the specificity of the method of the invention is linked to a set temperature of between 720°C and 900°C.

[0020] Preferably, the flash calcination step is carried out at a temperature of from 750°C to 860°C, and preferably from 810°C to 830°C. According to one embodiment, this step is carried out at 820°C.

[0021] The temperature mentioned here corresponds to a set temperature.

[0022] The method of the invention also makes it possible to “recycle” products obtained from washing sludge, particularly loaded with clay and limestone, which was stored in basins, as explained above.

[0023] The starting product of the process of the invention is therefore a clay-silico-limestone composition, namely therefore a composition comprising in particular a clay-silico-limestone filler.

[0024] By “clay-silico-limestone filler” is meant a mineral filler comprising in particular clay, silica and limestone.

[0025] According to one embodiment, said clay-silico-calcareous composition is obtained from washing water from processes for washing mineral materials, in particular from washing calcareous materials.

[0026] These washing waters (or sludges) are loaded with “undesirable” compounds, for conventional applications also called washing fines, and correspond to the waters obtained and stored after washing the limestone aggregates.

[0027] These wash waters are therefore in the form of a liquid solution, in which different minerals are present, such as clay, limestone or silica.

[0028] According to one embodiment, these wash waters comprise:

[0029] - from 10% to 45%, in particular from 12% to 40%, and preferably from 15% to 36%, mass of SiO2 relative to the total mass of said aqueous composition,

[0030] - from 1% to 20%, in particular from 3% to 15%, and preferably from 6.5% to 15%, by mass of A12O3 relative to the total mass of said aqueous composition, and

[0031] - from 25% to 85%, in particular from 30% to 81%, in particular from 34% to 70%, and preferably from 35% to 62%, by mass of limestone relative to the total mass of said aqueous composition.

[0032] For example, results obtained by X-ray fluorescence spectrometry and X-ray diffraction have shown that the solid fraction of these wash waters contained 36 to 78% calcium carbonate, 4 to 23% kaolinite, 4 to 17% illite / muscovite and 5% to 21% quartz. Other minerals may be present in small quantities (dolomite, goethite, anorthite, smectite, chlorite IA, interstratified illite / smectite and illite / chlorite).

[0033] According to one embodiment, the aforementioned clay-silico-limestone composition is obtained by a process comprising a step of filtration of the washing water as defined above, making it possible to obtain a filter cake, followed by a step of lumping and then drying said filter cake.

[0034] At the end of this process, the composition obtained is therefore in particular in solid form, and more particularly a powder.

[0035] The clay-silico-calcareous composition thus obtained therefore comprises in particular clay in various forms, quartz and chalcedony, and limestone (or calcium carbonate).

[0036] According to one embodiment, the clay-silico-limestone composition is in the form of a powder whose particle size is less than 200 μm.

[0037] By particle size is meant in particular the average diameter of said particles.

[0038] Preferably, the particle size of this powder is characterized by the d50 and / or by the d90. The d50 corresponds to the median of the distribution, i.e. 50% of the particles have a size less than the d50 and 50% have a size greater than the d50. The d90 corresponds to the 90th percentile of the particle size distribution, i.e. 90% of the particles have a size less than the d90 and 10% have a size greater than the d90.

[0039] The values ​​of d50 and / or d90 are notably measured by laser diffraction granulometry which is based on the interactions between light and matter. In a laser diffraction measurement, a laser beam passes through a sample of dispersed particles and the intensity of the scattered light is measured as a function of the angle. Large particles diffract light at small angles and small particles diffract low intensities at large angles. The diffracted intensities are then analyzed to calculate the particle size using an appropriate optical model. The particle size represents the diameter of the equivalent sphere having the same volume as the particle.

[0040] The d50 of the particles of the aforementioned powder is preferably less than 50 pm, or even less than 40 pm, or even less than 35 pm. Preferably, the d50 is between 5 and 15 pm. These d50 values ​​indicate that 50% of the particles have a size less than these d50 values.

[0041] The d90 of the particles of the aforementioned powder is preferably less than 200 pm, preferably less than 180 pm, and preferably greater than 20 pm, or even greater than 30 pm, and preferably greater than 35 pm. Preferably, the d90 is from 20 pm to 75 pm, in particular from 20 pm to 50 pm. These d90 values ​​indicate that 90% of the particles have a size less than these d90 values.

[0042] According to one embodiment, the clay-silico-limestone composition used in the process of the invention comprises kaolinite.

[0043] According to one embodiment, the clay-silico-limestone composition used in the process of the invention comprises more than 8% by mass of kaolinite relative to the total mass of said composition.

[0044] According to one embodiment, the kaolinite content in the clay-silico-limestone composition used in the process of the invention is less than 25%, or even less than 22%, by mass relative to the total mass of said composition.

[0045] Preferably, the clay-silico-limestone composition used in the process of the invention comprises from 3% to 30%, preferably from 8% to 25%, preferably from 10% to 22%, by mass of kaolinite relative to the total mass of said composition.

[0046] According to one embodiment, the method of the invention comprises a step of measuring the kaolinite content, for example by near infrared spectrometry.

[0047] The clay-silico-limestone composition used in the process of the invention may also comprise silica.

[0048] According to one embodiment, the clay-silico-limestone composition used in the process of the invention comprises from 5% to 35% by mass of silica relative to the total mass of said composition.

[0049] The silica content is notably measured by X-ray fluorescence spectrometry.

[0050] Preferably, the clay-silico-limestone composition used in the process of the invention comprises more than 8%, in particular more than 10%, preferably more than 15% by mass of silica relative to the total mass of said composition.

[0051] Preferably, the clay-silico-limestone composition used in the process of the invention comprises from 5% to 40%, in particular from 8% to 36%, and preferably from 15% to 30%, preferably from 15% to 25%, by mass of silica relative to the total mass of said composition.

[0052] The clay-silico-calcareous composition used in the process of the invention may also comprise alumina or A12O3.

[0053] The alumina content is notably measured by X-ray fluorescence spectrometry.

[0054] Preferably, the clay-silico-limestone composition used in the process of the invention comprises more than 3%, preferably more than 6.5%, by mass of A12O3 relative to the total mass of said composition.

[0055] According to one embodiment, the clay-silico-limestone composition comprises from 1% to 20%, in particular from 3% to 15%, and preferably from 6.5% to 10%, by mass of A12O3 relative to the total mass of said composition.

[0056] The clay-silico-calcareous composition used in the process of the invention comprises limestone.

[0057] The limestone content is measured in particular either by X-ray diffraction (XRD) (with rutile as internal standard, Rietveld method, TOPAS software) or by calculation from chemical analysis by X-ray fluorescence spectrometry according to the equation:

[0058] • % Calcite CaCO3 = (% CaO - % Dolomite * 56 / 184) * 100 / 56

[0059] With: M(CaO) = 56 g / mol

[0060] M(CaCO3) = 100 g / mol

[0061] % Dolomite CaMg(CO3)2 = % MgO * 184 / 40

[0062] M(MgO) = 40 g / mol

[0063] M(CaMg(CO3)2)=184 g / mol

[0064] Preferably, the clay-silico-limestone composition used in the process of the invention comprises more than 30%, or even preferably more than 45%, even more than 50%, preferably more than 55%, and preferentially more than 56%, by mass of limestone (in the form of calcium carbonate CaCO3) relative to the total mass of said composition.

[0065] According to one embodiment, the clay-silico-limestone composition used in the process of the invention comprises from 25% to 85%, in particular from 34% to 70%, and preferably from 35% to 70%, preferentially from 50% to 70%, by mass of limestone relative to the total mass of said composition.

[0066] According to one embodiment, the clay-silico-calcareous fillers used in the process of the invention comprise kaolinite.

[0067] According to one embodiment, the clay-silico-calcareous fillers comprise more than 8% by mass of kaolinite relative to the total mass of said fillers.

[0068] According to one embodiment, the kaolinite content in the clay-silico-calcareous fillers used in the process of the invention is less than 25%, or even less than 22%, by mass relative to the total mass of said fillers.

[0069] Preferably, the clay-silico-calcareous fillers used in the process of the invention comprise from 3% to 30%, preferably from 8% to 25%, preferably from 10% to 22%, by mass of kaolinite relative to the total mass of said fillers.

[0070] As indicated above, the process of the invention is particularly advantageous in that it makes it possible to recycle wash water, usually stored and not used, in order to also obtain a standardized product of interest, namely hydraulic lime.

[0071] According to one embodiment, the hydraulic lime obtained according to the process of the invention has a free lime content of at least 4% by weight.

[0072] According to one embodiment, the natural hydraulic lime obtained according to the process of the invention has a free lime content of at least 15% by weight.

[0073] By "free lime" is meant unbound lime in the form of calcium oxide and calcium hydroxide.

[0074] This content can be measured by different techniques, for example here it is extracted using acetoacetic ester and the extract is titrated with hydrochloric acid, bromophenol blue being used as an indicator.

[0075] Preferably, the hydraulic lime obtained according to the process of the invention has a compressive strength at 28 days of between 2 MPa and 20 MPa.

[0076] The compressive strength at 28 days is measured in particular according to standard NF EN 459-2:2021.

[0077] According to one embodiment, the hydraulic lime obtained according to the process of the invention comprises more than 25% by mass of amorphous phase.

[0078] The amorphous phase content is notably measured by X-ray diffraction (XRD) (with rutile as internal standard, Rietveld method, TOPAS software).

[0079] The amorphous phase is associated with pozzolanic reactivity, i.e. the capacity to form at ordinary temperature, in the presence of water, by combination with lime, stable hydrates capable of generating mechanical performance. EXAMPLES

[0080] Example 1: Preparation of a clay-silico-limestone composition

[0081] Here we use an average clay-silico-calcareous composition from the washing water of limestone aggregates from the Boulonnais Quarries.

[0082] This composition has the chemical composition according to Table 1 below (chemical analysis by RFX).

[0083] [Tables 1] SiO2 18.9% A12O3 7.2% Fe2O3 2.3% CaO 36.6% MgO 1.3% Na2O 0.07% k2o 0.82% TiO2 0.38% Mn2O3 0.04% PAF at 1000°C 32.3%

[0084] A dryer / deagglomerator was used to obtain a powdery and dry material. Its chemical composition was determined by X-ray fluorescence spectrometry which is an analytical technique allowing to obtain elementary quantitative analyses. Pelleting with a hydraulic press was used for sample preparation. A specific calibration was implemented.

[0085] The chemical composition of the powder obtained (chemical analysis by RFX) is that of table 1 above.

[0086] The mineralogical composition of the powder obtained was estimated from chemical analysis by X-ray fluorescence spectrometry (Rietveld method, TOPAS software) (see Table 2).

[0087] [Tables2] kaolinite 14% muscovite 4% illite 2% chlorite 2% quartz 10% calcite 57% dolomite 3% amorphous phase 10%

[0088] The methylene blue (MBF) value of 13 g / kg was determined in accordance with EN 933-9:2022.

[0089] The particle size curve of the powder before and after calcination was obtained from a laser particle sizer operating in the dry process. The values ​​obtained are as follows: D50 ~6.5 pm and D90 ~40 pm.

[0090] Example 2: Preparation of a natural hydraulic lime NHL 5 (Rc > 5 to <15 MPa at 28 days, Ca (OH) 2 >15%)

[0091] The clay-silico-calcareous composition of example 1 is subjected to a flash calcination step with reinjection of the fines from the bag filter into the calciner (Gas temperature = 1140°C, set temperature = 820°C).

[0092] The powder calcined under these conditions has the following characteristics and properties, corresponding to an NHL 5 lime:

[0093] [Tables3] SiO2 25.2% Reactive SiO2 (EN 197-1) 13.9% A12O3 9.5% Fe2O3 3.0% CaO 46.7% Free CaO (EN 451-1) 19.8% MgO 2.0% Na2O 0.12% k2o 1.29% TiO2 0.5% Cr2O3 0.02% MnO 0.08% SO3 0.28% PAF at 1000°C 11.7%

[0094] Table 4 below shows the mineralogical analysis (DRX) of the material obtained.

[0095] [Tables4] muscovite / illite 4% quartz 11% dolomite 1% calcite 20% amorphous phase 36% quicklime 22% periclase 0.4% hematite 1% belite 3.4% gehlenite 1.9%

[0096] The methylene blue (MBF) value of 1.3 g / kg was determined in accordance with EN 933-9:2022.

[0097] The diameters D50 and D90 were obtained by laser diffraction granulometry

[0098] [Tables5] Diameter D50 9 pm Diameter D90 40 pm

[0099] The color of the sample was measured using a Datacolor DC 200M colorimeter, according to the CIEL AB standard:

[0100] [Tableauxô] L ab Yellow index 63.2 11.8 21.1 62

[0101] The mechanical resistances were determined according to NF EN 459-2 “Construction Lime — Part 2: Test Methods”. The calcined powder was slaked before the design of the 4x4x16 test pieces.

[0102] The results obtained are shown in Table 7 below.

[0103] [Tables7] Water / Binder Ratio Strength at 28 days, MPa Unit Flexural Compression 0.6 3.7 ±0.3 12.7 ±0.1 MPa

[0104] Example 3: Preparation of a NHL 3.5 lime (Rc > 3.5 to <10 MPa at 28 days, Ca (OH) 2 >25%)

[0105] The clay-silico-calcareous composition of example 1 is subjected to a flash calcination step (without recovery of fines from the bag filter) in the calciner (Gas temperature = 1152°C, set temperature = 780°C).

[0106] The powder calcined under these conditions has the following characteristics and properties, corresponding to an NHL 3.5:

[0107] [Tables8] SiO2 25.0% Reactive SiO2 (EN 197-1) 11.9% A12O3 8.1% Fe2O3 2.6% CaO 45.0% Free CaO (EN 451-1) 26.0% MgO 1.9% Na2O 0.10% k2o 1.10% TiO2 0.4% Cr2O3 0.02% MnO 0.06% SO3 0.24% PAF at 1000°C 13.7%

[0108] The methylene blue (MBF) value of 2 g / kg was determined in accordance with EN 933-9:2022.

[0109] The particle size distribution was determined by air jet sieving according to NF EN 459-2.

[0110] [Tables9] % of cumulative passers-by 40 pm 63 pm 125 pm 250 pm 91.0 97.3 99.8 100

[0111] The product remains fine after calcination and without sintered particles.

[0112] The compressive strength at 28 days was measured according to NF EN 459-2 “Construction Lime — Part 2: Test Methods”. The calcined powder was slaked before the production of the 4x4x16 test pieces.

[0113] [TableauxlO] Water / Binder Ratio Compressive strength at 28 days, MPa 0.6 5.6 ±0.3

[0114] Example 4: Preparation of HL 5 lime (Rc > 5 to <15 MPa at 28 days, Ca (OH) 2 > 4%)

[0115] In order to reduce the carbon footprint, it is possible to use the calcined products at a lower temperature and / or to combine the calcined products according to the invention with materials with low environmental impact (for example blast furnace slag, natural pozzolan, calcium sulfate). These two possibilities then make it possible to obtain HL hydraulic lime.

[0116] A calcined powder was prepared by introducing the fines from the bag filter into the calciner (Gas temperature = 1100°C, set temperature = 790°C).

[0117] The powder calcined under these conditions has the following characteristics:

[0118] [Tables 11] SiO2 23.5% Reactive SiO2 (EN 197-1) 12.9% A12O3 9.2% Fe2O3 2.8% CaO 43.1% Free CaO (EN 451-1) 13.2% MgO 1.8% Na2O 0.10% k2o 1.17% TiO2 0.27% Cr2O3 0.44% MnO 0.01% SO3 0.06% PAF at 1000°C 17.4%

[0119] Table 12 below indicates the mineralogical analysis (DRX) of the material obtained.

[0120] [Tablesl2] muscovite / illite 5% quartz 10% dolomite 1% calcite 33% amorphous phase 32% quicklime 15% periclase 0.3% hematite 1% belite 3%

[0121] The methylene blue (MBF) value of 1.3 g / kg was determined in accordance with EN 933-9:2022.

[0122] In order to produce hydraulic lime, the powder thus calcined and characterized above is then mixed with 5% calcium sulfate.

[0123] The mixture obtained has the following characteristics:

[0124] The apparent density is 680 kg / m3.

[0125] The compressive strength at 28 days was measured according to NF EN 459-2 “ Construction Lime — Part 2: Test Methods ». The calcined powder was slaked before the 4x4x16 specimens were produced. In the case of the mixture of 95% powder calcined at 790°C and 5% calcium sulfate, a small quantity of SIKA POWER 800 superplasticizer was introduced into the mixing water (1.1% of the binder weight) in order to be able to mold the specimens with a water / binder ratio of 0.5 (required by the standard for an HL 5 with a density greater than 0.6 kg / dm3)•

[0126] [Tablesl3] Water / Binder Ratio Compressive strength at 28 days, MPa 0.5 20

[0127] Lime obtained from 95% powder calcined at 790°C and 5% calcium sulfate has an apparent density of less than 0.90 kg / dm3. The standard then authorizes a compressive strength at 28 days of up to 20 MPa. The addition of calcium sulfate facilitates demolding.

[0128] Example 5: Comparative example with calcination at 650°C

[0129] The clay-silico-limestone composition of example 1 is subjected to a flash calcination step (without recovery of the fines from the preheating stage in the calciner) at different temperatures, and in particular: - Gas temperature = 890°C, set temperature = 650°C - Gas temperature = 1152°C, set temperature = 780°C.

[0130] The powder calcined under these conditions has the following characteristics:

[0131] [Tables 14] 650°C 780°C SiO2 20.3% 25.0% Reactive SiO2 (EN 197-1) 8.8% 11.9% A12O3 6.8% 8.1% Fe2O3 2.1% 2.6% CaO 37.6% 45.0% Free CaO (EN 451-1) 0.7% 26.0% MgO 1.5% 1.9% Na2O 0.09% 0.10% k2o 0.86% 1.10% TiO2 0.3% 0.4% Cr2O3 0.01% 0.02% MnO 0.04% 0.06% SO3 0.11% 0.24% PAF at 1000°C 30.9% 13.7%

[0132] It is therefore noted that the product obtained is not lime when the calcination temperature is too low, and therefore less than 720°C.

Claims

Claims

1. Process for the preparation of hydraulic lime by flash calcination of a clay-silico-limestone composition, comprising a clay-silico-limestone filler, said flash calcination step being carried out at a temperature of from 720°C to 900°C, in particular from 750°C to 860°C, and preferably from 810°C to 830°C.

2. Preparation process according to claim 1, in which the clay-silico-limestone composition comprises more than 30%, or even preferably more than 45%, or even more than 50%, preferably more than 55%, by mass of calcium carbonate relative to the total mass of said composition.

3. Preparation process according to claim 1 or 2, in which the clay-silico-calcareous composition comprises more than 8% by mass of kaolinite relative to the total mass of said composition.

4. Preparation process according to any one of claims 1 to 3, in which the clay-silico-limestone composition comprises more than 8%, preferably more than 15% by mass of silica relative to the total mass of said composition.

5. Preparation process according to any one of claims 1 to 4, in which the clay-silico-limestone composition comprises more than 3%, preferably more than 6.5%, by mass of A12O3 relative to the total mass of said composition.

6. Preparation process according to any one of claims 1 to 5, in which the clay-silico-limestone composition is in the form of a powder whose particle size is less than 200 pm.

7. Preparation process according to any one of claims 1 to 6, in which the clay-silico-limestone composition is obtained from wash water from processes for washing mineral materials, in particular washing calcareous materials.