CN121219238A

CN121219238A - Method for controlling polymorphisms in PCC precipitated by CaCl2 and Na2CO3

Info

Publication number: CN121219238A
Application number: CN202480035654.XA
Authority: CN
Inventors: C·圣特纳; M·波尔
Original assignee: Omya International AG
Current assignee: Omya International AG
Priority date: 2023-05-31
Filing date: 2024-05-28
Publication date: 2025-12-26
Also published as: WO2024246045A1; EP4719990A1

Abstract

The present invention relates to a process for producing a scalenohedral PCC product, a scalenohedral PCC product obtainable by the process according to the present invention, and the use of a scalenohedral PCC product according to the present invention in polymer applications, paper coating applications, papermaking, paints, coatings, sealants, adhesives, feeds, pharmaceuticals, concrete, cements, cosmetics, water treatment, engineered wood applications, gypsum board applications, packaging applications, catalysis, gas treatment applications and/or agricultural applications.

Description

Method for polymorph control in PCC precipitated by CaCl 2 and Na 2CO3

Technical Field

Background

In recent years, calcium carbonate has a wide range of uses in many fields. For example, calcium carbonate is one of the most widely used minerals in the paper, plastic, paint and coating industries, both as a filler and as a pigment for a coating due to its white color. In the paper industry, calcium carbonate is valued for its high whiteness, opacity and gloss and is often used as a filler to make high whiteness opaque paper. In addition, calcium carbonate is often used as an extender in paints, and also as a filler in adhesives, sealants, and plastics. High grade calcium carbonate has also found use in pharmaceutical formulations or foods. In addition, calcium carbonate is often used in catalytic applications, gas treatment applications, water treatment and/or agricultural applications.

Calcium carbonate is known to exist in the form of naturally occurring minerals as well as synthetically produced products. Ground limestone (GCC) is calcium carbonate obtained from natural sources and processed by wet and/or dry treatment steps. Precipitated Calcium Carbonate (PCC) is a synthetic material obtained from a precipitation reaction. While naturally occurring Ground Calcium Carbonate (GCC) is commonly used as a filler in many applications, synthetically produced Precipitated Calcium Carbonate (PCC) may be tailored, particularly in terms of its morphology or particle size, allowing the PCC to perform additional functions.

In general, one way of commercially producing precipitated calcium carbonate is to obtain quicklime by calcining coarse limestone. Water is then added to give an aqueous suspension of calcium hydroxide ("lime cream") (this reaction is shown in reaction (1)) and carbon dioxide is reintroduced into the slurry to precipitate calcium carbonate (this reaction is shown in reaction (2)).

(1) CaO+H ₂O → Ca(OH)₂ +heat

(2) Ca (OH) ₂ + CO₂ → CaCO₃ + H₂ O+ heat

The product of this process is known as precipitated calcium carbonate ("PCC"). The resulting aqueous suspension or slurry of calcium carbonate may be used as such or further processed (e.g., dewatered, ground, depolymerized, etc.) to form a dried product. Depending on the exact reaction conditions, the precipitation reaction can produce calcium carbonate with different properties.

US5811070a discloses a process for producing precipitated calcium carbonate particles comprising the steps of introducing carbon dioxide into a milk of lime comprising a first reagent to prepare an aqueous suspension comprising calcium carbonate particles having an average size of 0.4 μm, adding the milk of lime to the aqueous suspension, and continuously reacting a carbonated solution comprising a second reagent with the aqueous suspension.

EP1631525A1 discloses a process for the preparation of precipitated calcium carbonate in tablet form comprising the steps of providing a calcium hydroxide suspension, carbonating the calcium hydroxide suspension, adding polyacrylate to the suspension before carbonation is completed to obtain precipitated calcium carbonate in tablet form.

US2006/0196836A1 describes a method for treating seven types of brine. The method includes the step of contacting water with a first reagent comprising a source of calcium ions selected from the group consisting of calcium oxide and calcium hydroxide to form a recovered first solid product. The method includes the further step of subjecting at least a portion of the partially treated water to at least partial evaporation to promote the formation of precipitate and mother liquor. The precipitate is recovered as a second product.

Technical problem

However, in the known process of reaction step (1), only calcium oxide is used as a source for producing calcium hydroxide (also called "milk of lime") and subsequently precipitated calcium carbonate. Furthermore, in the reaction step (2), carbon dioxide is introduced into this slurry to precipitate calcium carbonate. Today, it is often desirable to use different sources of calcium for more flexibility and in particular to use at least one source of calcium different from calcium oxide and milk of lime. Furthermore, the use of carbon dioxide as a gas generally results in significantly more complex and expensive equipment. Furthermore, methods with an increased carbon dioxide footprint are disadvantageous and often rejected by the manufacturer.

Furthermore, due to the continued preference for ecologically and environmentally friendly products, it is preferred that the educts (educts) can be prepared or obtained from recycled materials such as waste materials.

In addition to this, monitoring and control of the above-described reactions is often difficult, and therefore undesirable morphologies, or even mixtures of different morphologies, are sometimes obtained. This is disadvantageous because in many areas, customized Precipitated Calcium Carbonate (PCC), especially in terms of its morphology, is required, sometimes also in terms of particle size or surface area, to achieve additional functionality.

Accordingly, there is a continuing need for methods for providing precipitated calcium carbonate products that overcome at least one of the above-described drawbacks, and in particular methods that allow for controlling the morphology of the precipitated calcium carbonate product.

Disclosure of Invention

Object of the Invention

It is therefore an object of the present invention to provide a process for producing a precipitated calcium carbonate product having a defined morphology, i.e. a process for producing scalenohedral PCC products. Scalenohedral PCC exhibits triangular clusters of crystals emanating from a central core (rosettes (rosettes)).

It is another object of the present invention to provide a method for producing precipitated calcium carbonate using different calcium sources. In particular, it is an object of the present invention to provide a method for producing precipitated calcium carbonate using at least one calcium source different from calcium oxide and milk of lime.

Furthermore, it is an object of the present invention to provide a process for producing precipitated calcium carbonate products which is inexpensive, easy to handle and easy to adapt. It is particularly desirable that the process for producing precipitated calcium carbonate products have a reduced carbon dioxide footprint and do not use carbon dioxide containing compounds, especially gaseous carbon dioxide. Furthermore, it is desirable to obtain toxic or hazardous chemicals without use or as a by-product.

The foregoing and other objects are solved by the subject matter as defined herein in the independent claims.

According to an embodiment of the present invention, there is provided a process for producing scalenohedral PCC products, the process comprising the steps of:

a) Providing at least one calcium compound selected from the group consisting of calcium oxide powder, calcium hydroxide powder and calcium hydroxide suspension;

b) Providing a calcium chloride solution, wherein the solution comprises 0.5-270g/l calcium;

c) Mixing the at least one calcium compound of step a) and the calcium chloride solution of step b) in any order,

Wherein the molar amount of the at least one calcium compound of step a) and the calcium chloride of step b) in the obtained mixture is from 7:93 to 80:20;

d) Adding a sodium carbonate source selected from sodium carbonate or a mixture consisting of at least 70% by weight sodium carbonate and at most 30% by weight sodium bicarbonate to the mixture obtained in step C) at a temperature of 30-70 ℃ and at a pH value of 9.5-13.5,

Wherein the sum of the calcium-containing materials of steps a) and b) and the sodium carbonate source of step d) have a molar ratio of calcium ions to carbonate ions (Ca ²⁺:CO₃ ^2-) of from 1.00:1.00 to 1.00:1.30.

The inventors have unexpectedly found that by the above process it is possible to control the morphology of the precipitated calcium carbonate and obtain a scalenohedral PCC product. Furthermore, the inventors have found that calcium chloride can be used as an additional calcium source in addition to calcium oxide or lime milk. In addition, the inventors have unexpectedly found that no carbon dioxide containing compounds, in particular no gaseous carbon dioxide, are required to obtain a scalenohedral PCC product in the process of the present invention. But rather a sodium carbonate source selected from sodium carbonate or a mixture consisting of at least 70% by weight sodium carbonate and at most 30% by weight sodium bicarbonate, is sufficient to produce a scalenohedral PCC product at the temperatures and pH values described above. Thus, the inventive process has a reduced carbon dioxide footprint and is inexpensive, easy to handle and easy to adjust to accommodate. In this method, no chemicals that are toxic or harmful to the user are used. In addition, the by-products obtained in this process are also non-toxic or harmless and can even be recovered for subsequent use, for example sodium chloride.

According to another embodiment of the present invention, there is provided a scalenohedral PCC product obtainable according to the process of the present invention.

According to another embodiment of the present invention, the inventive scalenohedral PCC product obtainable according to the process of the present invention is used in polymer applications, paper coating applications, papermaking, paints, coatings, sealants, adhesives, feeds, pharmaceuticals, concrete, cements, cosmetics, water treatment, engineered wood applications, gypsum board applications, packaging applications, catalysis, gas treatment applications and/or agricultural applications.

Advantageous embodiments of the invention are defined in the respective dependent claims.

According to one embodiment of the invention, the at least one calcium compound of step a) is a calcium hydroxide powder or a calcium hydroxide suspension, preferably a calcium hydroxide suspension, and preferably the calcium hydroxide suspension has a solids content of 5-50% by weight, preferably 7-47% by weight and most preferably 9-45% by weight, based on the total weight of the calcium hydroxide suspension.

According to another embodiment of the invention, the at least one calcium compound of step a) is in the form of calcium hydroxide particles having a volume median particle size d ₅₀ (vol) of 0.05-25 μm, preferably 0.2-10 μm, more preferably 0.4-5 μm and most preferably 1.0-3.5 μm, and/or a volume-based particle size d ₉₀ (vol) of 0.15-75 μm, preferably 1-30 μm, more preferably 1.5-15 μm and most preferably 2-10 μm.

According to another embodiment of the invention, the calcium chloride solution of step b) comprises 1.0-200g/l, preferably 2.0-150g/l, more preferably 3.0-100g/l and most preferably 5.0-50g/l of calcium.

According to another embodiment of the invention, the molar amount of the at least one calcium compound of step a) and the calcium chloride of step b) in the obtained mixture in step c) is from 10:90 to 70:30, preferably from 15:85 to 50:50, more preferably from 20:80 to 40:60 and most preferably about 25:75.

According to another embodiment of the invention, the temperature in step d) is 40-60 ℃, more preferably 45-50 ℃ and/or wherein the pH is 10.0 to 13.0 and more preferably 10.5 to 12.0.

According to another embodiment of the invention, the sodium carbonate source is added in at least two portions to the mixture obtained in step c),

Wherein the first part comprises 0.01-5% by weight of the total amount of the sodium carbonate source and is added in the form of a solution comprising 5-20g/l of the sodium carbonate source, preferably wherein the first part of the sodium carbonate source in step d) comprises 0.1-4.0% by weight, more preferably 1.0-3.0% by weight and most preferably 1.5-2.5% by weight of the total amount of the sodium carbonate source, and/or

Added in the form of a solution comprising 7-17g/l, preferably 8-15g/l of the sodium carbonate source.

According to another embodiment of the invention, the sodium carbonate source remaining after the first part is added as a second part in one part, and/or wherein the sodium carbonate source remaining after the first part is added as a solid, and/or

The sodium carbonate source is sodium carbonate.

According to another embodiment of the invention, the sum of the calcium-containing materials of steps a) and b) and the sodium carbonate source of step d) have a molar ratio of calcium ions to carbonate ions (Ca ²⁺:CO₃ ^2-) of 1.00:1.00 to 1.00:1.20, more preferably 1.00:1.00 to 1.00:1.10 and most preferably about 1.00:1.05.

According to another embodiment of the invention, the method further comprises a step e) of adding additives, preferably dispersants and/or nucleating agents, such as sucrose or citrate, and most preferably sucrose, to the mixture obtained in step c).

According to another embodiment of the invention, the process further comprises a step f) of separating the scalenohedral PCC product from the aqueous suspension obtained in step d), and preferably, step f) is performed by solvent evaporation and/or pressure filtration, and/or

Wherein the process further comprises a step g) of drying the scalenohedral PCC product after step d) or after step f) if present at a temperature of 60-120 ℃, preferably 80-110 ℃ and most preferably 95-105 ℃, preferably until the moisture content of the scalenohedral PCC product is less than 1% by weight, based on the total weight of the dried scalenohedral PCC product.

According to another embodiment of the invention, the calcium chloride solution in step b) is a waste material, preferably obtained from a recycling process, and more preferably obtained from an aqueous phosphor recycling process, and/or wherein the calcium chloride solution comprises a further salt, preferably selected from magnesium salts, sodium salts and potassium salts and most preferably selected from magnesium chloride, sodium chloride and potassium chloride.

According to another embodiment of the invention, the calcium chloride solution in step b) comprises magnesium salts, and preferably the solution comprises 5-200mg/l, more preferably 5-100mg/l and most preferably 5-50mg/l magnesium.

According to another embodiment of the invention, a scalenohedral PCC product is obtained

I) Has a specific surface area of 0.1 to 25.0m ²/g, preferably 0.5 to 20.0m ²/g and most preferably 1.0 to 15.0m ²/g, measured according to ISO 9277:2010 using nitrogen and BET methods, and/or

Ii) is in the form of particles having a volume-based median particle size d ₅₀ (vol) of 0.05 to 10 μm, preferably 0.2 to 8 μm, more preferably 0.4 to 5 μm and most preferably 1.0 to 3.5 μm, and/or

Iii) In the form of particles having a volume-based top-cut particle size d ₉₈ (vol) of 0.15-20 μm, preferably 1-15 μm, more preferably 1.5-10 μm and most preferably 2-8 μm, and/or

Iv) has an ISO whiteness (R457) of at least 90%, preferably at least 92%, more preferably at least 95% and most preferably at least 97%, and/or

V) a Yellowness Index (YI) of less than 2, preferably less than 1.8, more preferably less than 1.6 and most preferably from 0.5 to 1.5, and/or

Vi) comprises at least 80 wt%, preferably 90 wt% and most preferably 95 wt% scalenohedral PCC based on the total dry weight of the scalenohedral PCC product, and 20 wt% or less, preferably 10 wt% or less and most preferably 5 wt% or less aragonite based on the total dry weight of the scalenohedral PCC product.

It is to be understood that for the purposes of the present invention, the following terms have the following meanings:

"calcium carbonate-containing material" within the meaning of the present invention is a mineral or synthetic material comprising a calcium carbonate content of at least 80% by weight, preferably 85% by weight, more preferably 90% by weight and most preferably 95% by weight, based on the total weight of the calcium carbonate-containing material.

"Natural ground calcium carbonate" (GCC, also referred to as GNCC) within the meaning of the present invention refers to calcium carbonate obtained from natural sources (e.g. limestone, marble or chalk) and processed by wet and/or dry treatments such as grinding, screening and/or classification (e.g. by means of cyclones or classifiers).

"Precipitated calcium carbonate" (PCC) within the meaning of the present invention is a synthetic material, which is generally obtainable by precipitation after reaction of carbon dioxide with calcium hydroxide (slaked lime) in an aqueous environment (milk of lime) or by precipitation of calcium and carbonate sources in water. Additionally, precipitated calcium carbonate may also be the product of the incorporation of calcium salts and carbonates such as calcium chloride and sodium carbonate in an aqueous environment. The PCC may be vaterite, calcite or aragonite or a mixture thereof. PCC is described, for example, in EP2447213A1, EP2524898A1, EP2371766A1 or WO2013/142473A1.

"Scalenohedral PCC" in the meaning of the present invention is a calcite-form PCC having a trigonal structure with scalenohedral crystal habit. Scalenohedral PCC exhibits triangular clusters of crystals (rosettes) emanating from a central core.

"Calcium oxide" in the meaning of the present invention is a compound having the formula CaO and consisting of calcium ions and oxide ions.

"Calcium hydroxide" in the meaning of the present invention is a compound having the formula Ca (OH) ₂ and consisting of calcium ions and hydroxide ions.

"Calcium chloride" in the meaning of the present invention is a compound having the formula CaCl ₂ and consisting of calcium ions and chloride ions.

"Sodium carbonate" in the meaning of the present invention is a compound having the formula Na ₂CO₃ and consisting of sodium ions and carbonate ions. It is also known as wash alkali, soda ash and soda crystallization.

"Sodium bicarbonate" in the meaning of the present invention is a compound having the formula NaHCO ₃ and consisting of sodium ions and bicarbonate ions. It is also known as baking soda or sodium bicarbonate.

Throughout this document, the "particle size" of the particulate material, except for the scalenohedral PCC product and calcium hydroxide obtained herein, is described by its particle size distribution d _x (wt). Wherein the value d _x (wt) represents the diameter relative to which x% by weight of the particles have a diameter smaller than d _x (wt). This means, for example, that the value d ₂₀ (wt) refers to a particle size in which 20% by weight of all particles are smaller than this particle size. The d ₅₀ (wt) value is thus the weight median particle size, i.e. 50% by weight of all particles is smaller than the particle size, and the d ₉₀ (wt) value refers to the particle size in which 90% by weight of all particles is smaller than the particle size. The weight-based median particle size d ₅₀ (wt) and the weight-based particle size d ₉₀ (wt) are measured by a sedimentation method, which is an analysis of sedimentation behavior in a gravitational field. Measurements were made using the Sedigraph ^TM 5120 of us Micromeritics Instrument Corporation. Methods and instruments are known to those skilled in the art and are commonly used to determine particle size distribution. Measurements were made in an aqueous solution of 0.1% by weight Na ₄P₂O₇. High speed agitators and sonication were used to disperse the sample.

The "particle size" of the scalenohedral PCC product and calcium hydroxide obtained herein is described as the volume-based particle size distribution d _x (vol). Wherein the value d _x (vol) represents the diameter relative to which x% by volume of the particles have a diameter smaller than d _x (vol). This means, for example, that the d ₂₀ (vol) value refers to the particle size in which 20% by volume of all particles are smaller than this particle size. The d ₅₀ (vol) value is thus the volume median particle size, i.e. 50% by volume of all particles is smaller than the particle size, the d ₉₀ (vol) value is thus the value where 90% by volume of all particles is smaller than the particle size, and the d ₉₈ (vol) value, referred to as volume base cut, is the particle size where 98% by volume of all particles is smaller than the particle size. The volume median particle size d ₅₀ was assessed using a HELOS particle size analyzer and software windows of Sympatec GmbH. The particle size of the obtained scalenohedral PCC product was measured in water, and the particle size of calcium hydroxide was measured in analytically pure ethanol. The d ₅₀、d₉₀ or d ₉₈ value measured using a HELOS particle size analyzer and software windows of Sympatec GmbH represents a diameter value such that 50%, 90% or 98% by volume of the particles, respectively, have a diameter less than that value. Raw data obtained by measurement were analyzed using the Mie (Mie) theory, in which the refractive index of particles is 1.57 and the absorption index is 0.005. Alternatively, malvern Mastersizer 3000,3000 laser diffraction systems may be used.

Throughout this document, the term "specific surface area" (m ²/g) used to define functionalized calcium carbonate or other materials refers to the specific surface area determined by using the BET method (using nitrogen as the absorbing gas). The BET method is well known to those skilled in the art (ISO 9277:2010). The total surface area (m ²) of the filler material is then obtained by multiplying the specific surface area of the corresponding sample by the mass (g).

The term "whiteness" as used in the context of the present invention is a measure of the percentage of diffuse light reflected from a powder tablet produced from a PCC product. The brighter the PCC product the more diffuse light is reflected. As used herein, the whiteness of a PCC product can be measured at a wavelength of light of 457nm (R457) and is specified in percent.

"Yellowness Index (YI)" as used in the context of the present invention is measured in accordance with DIN 6167. The Yellowness Index (YI) is a number calculated from spectrophotometric data that describes the change in color of a test sample from clear or white to yellow.

For the purposes of the present invention, the term "viscosity" or "brookfield viscosity" refers to the brookfield viscosity. For this purpose, the Brookfield viscosity is measured by a Brookfield DV-II+Pro viscometer at 25.+ -. 1 ℃ using a suitable rotor of the Brookfield RV-rotor group, and specified as mPa, at 100 rpmS. The person skilled in the art will, based on his technical knowledge, select from the Brookfield RV-rotor set a rotor suitable for the viscosity range to be measured. For example, for 200-800mPaViscosity in the range between s, rotor number 3 can be used for a viscosity in the range 400-1600mPaViscosity range between s, rotor number 4, for 800-3200mPaViscosity in the range between s, rotor number 5 can be used for 1000-2000000mPaThe viscosity range between s, rotor number 6 can be used, and for 4000-8000000mPaA viscosity range between s, rotor number 7 may be used.

For the purposes of the present invention, the "solids content" of a liquid composition is a measure of the amount of material remaining after all solvent or water has evaporated. If desired, the "solids content" of the suspension given in% by weight in the sense of the present invention can be determined using Halogen Moisture Analyzer HR73 (t=160 ℃, auto-off 3, standard dry) from Mettler-Toledo with a sample size of 5-20 g.

The term "drying" refers, unless otherwise indicated, to a process according to which at least a portion of the water is removed from the material to be dried such that a constant weight of the "dried" material obtained at 160 ℃ is reached. The term "dry" material or "dry" composition is understood to mean a material/composition having less than 1.0% by weight of water, relative to the weight of the material/composition. The% water was determined at a sample size of 5-20 g using Halogen Moisture Analyzer HR73 (t=160 ℃, auto shut off 3, standard dry) from Mettler-Toledo.

"Powder" in the sense of the present invention is a dry material in the form of particles.

"Suspensions" or "slurries" in the sense of the present invention comprise undissolved solids and liquids, and optionally other additives, and generally comprise a large amount of solids, and are thus more viscous and may have a higher density than the liquid from which they were formed.

When the term "comprising" is used in this specification and claims, it does not exclude other elements. For the purposes of the present invention, the term "consisting of" is considered to be a preferred embodiment of the term "comprising" or "comprising". If in the following it is defined that a group set (group) comprises at least a certain number of embodiments, this is also to be understood as disclosing a group set, which preferably consists of only these embodiments.

Where an indefinite or definite article is used when referring to a singular noun, e.g. "a", "an" or "the", this includes a plural of that noun unless something else is specifically stated.

Terms such as "available (obtainable)" or "definable (definable)" and "obtained (obtained)" or "defined (defined)" are used interchangeably. This means, for example, that the term "obtained" is not meant to indicate that, for example, an embodiment must be obtained by, for example, the sequence of steps following the term "obtained" unless the context clearly indicates otherwise, although the term "obtained" or "defined" always includes such a limiting understanding as a preferred embodiment.

Detailed description of the invention

The inventive process for producing scalenohedral PCC products comprises the steps of:

a) providing at least one calcium compound selected from the group consisting of calcium oxide powder, calcium hydroxide powder and calcium hydroxide suspension, b) providing a calcium chloride solution, wherein the solution comprises 0.5-270g/l of calcium, C) mixing the at least one calcium compound of step a) and the calcium chloride solution of step b) in any order, wherein the molar amount of the at least one calcium compound of step a) to the calcium chloride of step b) in the obtained mixture is 7:93 to 80:20, and d) adding a sodium carbonate source selected from the group consisting of sodium carbonate or a mixture consisting of at least 70% by weight of sodium carbonate and up to 30% by weight of sodium bicarbonate to the mixture obtained in step C) at a temperature of 30-70 ℃ and a pH value of 9.5-13.5, wherein the sum of the calcium-containing materials of steps a) and b) and the sodium carbonate source of step d) have a molar ratio of calcium ions to carbonate ions (Ca ²⁺:CO₃ ^2-) of 1.00:1.00 to 1.00:1.30:30.

Preferred embodiments of the process of the present invention for producing scalenohedral PCC products will be described in more detail below. It is to be understood that these embodiments and details also apply to the product of the invention and its use.

Method step a)

In step a) of the method of the present invention, at least one calcium compound is provided, which is selected from the group consisting of calcium oxide powder, calcium hydroxide powder and calcium hydroxide suspension.

The calcium oxide powder of step a) may be obtained by calcining a calcium carbonate-containing material. Calcination is a heat treatment process applied to calcium carbonate-containing materials to cause thermal decomposition, resulting in the formation of calcium oxide and gaseous carbon dioxide. Calcium carbonate-containing materials useful in this calcination process are those selected from precipitated calcium carbonate, natural calcium carbonate-containing minerals such as marble, limestone and chalk, and mixed alkaline earth carbonate minerals comprising calcium carbonate such as dolomite, or calcium carbonate-rich fractions from other sources. The waste material comprising calcium carbonate may also be subjected to a calcination treatment to obtain a calcium oxide-containing material.

Calcium carbonate decomposes to calcium oxide (commonly referred to as quicklime) at about 1000 ℃. The calcination step may be performed under conditions and using equipment known to those skilled in the art. In general, calcination may be carried out in furnaces or reactors (sometimes referred to as kilns) of various designs, including shaft furnaces, rotary kilns, multiple hearth furnaces, and fluidized bed reactors.

The end of the calcination reaction can be determined, for example, by monitoring the density change, the residual carbonate content (for example by X-ray diffraction) or the digestion reactivity (by customary methods).

According to one embodiment of the invention, the calcium oxide-containing material is obtained by calcining a calcium carbonate-containing material, preferably selected from precipitated calcium carbonate, natural calcium carbonate minerals such as marble, limestone and chalk, mixed alkaline earth carbonate minerals comprising calcium carbonate such as dolomite, and mixtures thereof, and most preferably obtained by calcining natural calcium carbonate minerals such as marble, limestone and chalk.

For efficiency reasons, it is preferred that the calcium oxide powder has a minimum calcium oxide content of at least 75% by weight, preferably at least 90% by weight and most preferably 95% by weight, based on the total weight of the calcium oxide powder. According to one embodiment, the calcium oxide powder consists of calcium oxide.

The calcium oxide powder may consist of only one type of calcium oxide powder. Alternatively, the calcium oxide powder may be composed of a mixture of two or more types of calcium oxide powder.

The calcium oxide-containing material is ground prior to use to obtain crushed calcium oxide particles or calcium oxide powder. In general, the dry milling step may be performed, for example, with any conventional milling apparatus under conditions such that comminution results primarily from impact with an auxiliary body, i.e., in one or more of a ball mill, rod mill, vibratory mill, crusher, centrifugal impact mill, vertical bead mill, attritor, pin mill, hammer mill, pulverizer, shredder, deblock, cutter (knife cutter), or other such devices known to those skilled in the art. It is also common that such calcium oxide-containing materials undergo a beneficiation step, such as magnetic separation, after milling to remove impurities.

According to one embodiment of the invention, the crushed calcium oxide is in the form of particles having a weight median particle size d ₅₀ (wt) of 20-100mm, preferably 20-90mm and most preferably 20-70mm. Such crushed calcium oxide is also known to those skilled in the art as slaked lime and is commercially available.

According to another embodiment of the invention, the crushed calcium oxide is in the form of particles having a weight median particle size d ₅₀ (wt) of 0.5-20mm, preferably 1-20mm. Such crushed calcium oxide is also known to those skilled in the art as pebble lime and is commercially available.

According to another embodiment of the invention, the calcium oxide powder is in the form of particles having a weight median particle size d ₅₀ (wt) of 0.05-90 μm, preferably 0.05-50 μm. According to another embodiment of the invention, the calcium oxide powder is in the form of particles having a weight median particle size d ₅₀ (wt) of 0.05-25 μm, preferably 0.2-10 μm, more preferably 0.4-5 μm and most preferably 1.0-3.5 μm.

Additionally or alternatively, the calcium oxide powder is in the form of particles having a particle size d ₉₀ (wt) of 0.15-75 μm, preferably 1-30 μm, more preferably 1.5-15 μm and most preferably 2-10 μm.

According to one embodiment of the invention, the calcium oxide powder of step a) consists of calcium oxide and is in the form of particles having a weight median particle size d ₅₀ (wt) of 0.05-25 μm, preferably 0.2-10 μm, more preferably 0.4-5 μm and most preferably 1.0-3.5 μm, and a particle size d ₉₀ (wt) of 0.15-75 μm, preferably 1-30 μm, more preferably 1.5-15 μm and most preferably 2-10 μm.

The calcium hydroxide powder and the calcium hydroxide suspension of step a) may be prepared by mixing water and a calcium oxide containing material. Preferably, the calcium oxide-containing material and water are mixed in a weight ratio of 1:1 to 1:12 (e.g., in a weight ratio of 1:3 to 1:12 or 1:5 to 1:10).

The reaction of the calcium oxide-containing material with water results in the formation of a milky calcium hydroxide suspension, better known as lime milk. The reaction is highly exothermic and is also known in the art as "lime slaking".

The temperature of the water used to digest the calcium oxide-containing material is adjusted to be in the range of greater than 0 ℃ and less than 100 ℃. In other words, the water used to digest the calcium oxide-containing material is adjusted to a temperature range in which the water is in liquid form. Preferably, the temperature of the water is adjusted to 1 ℃ to 70 ℃, more preferably 2 ℃ to 50 ℃, even more preferably 30 ℃ to 50 ℃, and most preferably 35 ℃ to 45 ℃.

According to a preferred embodiment, "lime digestion" is carried out under mixing, agitation or stirring (e.g., mechanical stirring). Suitable process equipment for mixing, agitating or stirring are known to those skilled in the art.

The progress of the digestion reaction can be observed by measuring the temperature and/or conductivity of the reaction mixture. It can also be monitored by turbidity control. Alternatively or additionally, the progress of the digestion reaction may be visually inspected.

According to a preferred embodiment of the invention, the calcium hydroxide suspension has a solids content of 5-50% by weight, preferably 7-47% by weight and most preferably 9-45% by weight, based on the total weight of the calcium hydroxide suspension.

Additionally or alternatively, the calcium hydroxide suspension has a Brookfield viscosity of 1-1000mPa at 25 DEG CS, more preferably 5-800mPa at 25 DEG CS and most preferably 10-500mPa at 25 DEG CS. According to one embodiment, the brookfield viscosity is measured at 100 rpm.

According to one embodiment, the calcium hydroxide is separated from the calcium hydroxide suspension. The separation may be carried out by any conventional separation means known to those skilled in the art, such as mechanical and/or thermal separation. Examples of mechanical separation processes are filtration, for example by means of rotary drum filters or filter presses, nanofiltration or centrifugation. An example of a thermal separation process is a concentration process by applying heat, for example in an evaporator.

After separation, the calcium hydroxide may be dried to obtain a calcium hydroxide powder. The drying may be carried out at a temperature of 60-120 ℃, preferably 80-100 ℃, preferably until the moisture content of the calcium hydroxide powder is less than 1% by weight, based on the total weight of the dried calcium hydroxide. The drying may include, for example, thermal drying and/or reduced pressure drying, using equipment such as an evaporator, flash dryer, oven, spray dryer, and/or drying in a vacuum chamber. The drying step f) may be carried out under reduced pressure, ambient pressure or increased pressure. The drying time can be selected by one skilled in the art depending on the equipment, water content and intended use.

For efficiency reasons, it is preferred that the calcium hydroxide powder has a minimum calcium hydroxide content of at least 75% by weight, preferably at least 90% by weight and most preferably 95% by weight, based on the total weight of the calcium hydroxide powder. According to one embodiment, the calcium hydroxide powder consists of calcium hydroxide.

The calcium hydroxide powder may consist of only one type of calcium hydroxide powder. Alternatively, the calcium hydroxide powder may be composed of a mixture of two or more types of calcium hydroxide powder.

According to a preferred embodiment, the calcium hydroxide powder is in the form of particles having a volume median particle size d ₅₀ (vol) of 0.05 to 25 μm, preferably 0.2 to 10 μm, more preferably 0.4 to 5 μm and most preferably 1.0 to 3.5 μm.

Additionally or alternatively, the calcium hydroxide powder is in the form of particles having a volume-based particle size d ₉₀ (vol) of 0.15-75 μm, preferably 1-30 μm, more preferably 1.5-15 μm and most preferably 2-10 μm.

According to a preferred embodiment of the invention, the calcium hydroxide powder of step a) consists of calcium hydroxide and is in the form of particles having a volume median particle size d ₅₀ (vol) of 0.05-25 μm, preferably 0.2-10 μm, more preferably 0.4-5 μm and most preferably 1.0-3.5 μm and a volume-based particle size d ₉₀ (vol) of 0.15-75 μm, preferably 1-30 μm, more preferably 1.5-15 μm and most preferably 2-10 μm.

Method step b)

In step b) of the process of the present invention, a calcium chloride solution is provided, wherein the solution comprises 0.5-270g/l calcium.

The calcium chloride solution of step b) may be obtained by dissolving calcium chloride in water. According to a preferred embodiment of the invention, the calcium chloride solution is an aqueous solution and the solvent consists of water only.

Alternatively, the solvent comprises water and in addition thereto a minor amount of at least one water miscible organic solvent selected from the group consisting of methanol, ethanol, acetone, acetonitrile, tetrahydrofuran and mixtures thereof. If the solution comprises water and at least one water-miscible organic solvent, the at least one water-miscible organic solvent is present in an amount of 0.1 to 40.0% by weight, preferably 0.25 to 30.0% by weight, more preferably 0.5 to 20.0% by weight and most preferably 1.0 to 10.0% by weight, based on the total weight of the solvent.

The calcium chloride solution of step b) comprises 0.5-270g/l calcium. According to a preferred embodiment of the invention, the calcium chloride solution of step b) comprises 1.0-200g/l, preferably 2.0-150g/l, more preferably 3.0-100g/l and most preferably 5.0-50g/l, e.g. 15-50g/l or 25-50g/l calcium.

According to another embodiment of the invention, the calcium chloride solution comprises calcium chloride in an amount of 0.1-60% by weight, preferably in an amount of 0.3-50% by weight, more preferably in an amount of 0.5-36% by weight, even more preferably in an amount of 0.8-22% by weight, and most preferably in an amount of 1.4-12% by weight, based on the total weight of the aqueous solution.

The calcium chloride solution of step b) may be obtained by dissolving calcium chloride in water. Alternatively, the calcium chloride solution of step b) is obtained from waste material. For example, the calcium chloride solution may be obtained from a recycling process. Recycling processes that provide calcium chloride solution are known to those skilled in the art. According to a preferred embodiment, the recycled calcium chloride solution is obtained from an aqueous phosphor recycling process.

According to another embodiment of the invention, the calcium chloride solution of step b) comprises other salts, preferably selected from magnesium salts, sodium salts and potassium salts and most preferably selected from magnesium chloride, sodium chloride and potassium chloride.

The additional salts may each be present in the calcium chloride solution in an amount of 10-500mg/l, more preferably 15-300mg/l and most preferably 15-200mg/l of magnesium, sodium and potassium.

According to a preferred embodiment of the invention, the calcium chloride solution of step b) comprises magnesium salts. For example, the calcium chloride solution comprises, preferably consists of, water, calcium chloride and magnesium salt. According to a preferred embodiment, the calcium chloride solution of step b) comprises magnesium salts, and preferably the solution comprises 5-200mg/l, more preferably 5-100mg/l and most preferably 5-50mg/l magnesium.

Method step c)

In step c) of the present invention, the at least one calcium compound of step a) and the calcium chloride solution of step b) are mixed in any order. In the mixture obtained, the molar amount of the at least one calcium compound of step a) and the calcium chloride of step b) is in the range of 7:93 to 80:20.

According to one embodiment of the invention, step c) comprises the step of providing the at least one calcium compound of step a) and then adding the calcium chloride solution of step b). According to another embodiment of the invention, step c) comprises the step of providing the calcium chloride solution of step b) and then adding the at least one calcium compound of step a).

The second component may be added in one portion or may be added in several equal or unequal portions, i.e. in larger and smaller portions.

Additional water may be added to the resulting mixture of step c).

The mixing or contacting or combining of the at least one calcium compound of step a) with the calcium chloride solution of step b) may be achieved by any conventional means known to the person skilled in the art. Preferably, the mixing may be performed using a wet mill, a mixing tank, a feed pump, or a flotation stirrer.

The mixing may be performed at room temperature or other temperatures. According to one embodiment, the mixing may be carried out at a temperature of 5-80 ℃, preferably 10-70 ℃ and most preferably 20-65 ℃ or at other temperatures. For example, the mixing may be performed at 60±2 ℃. The heat may be introduced by internal shear or by an external source or a combination thereof.

The mixing step may be performed for example for at least 30 seconds, at least 1 minute, 2 minutes, 5 minutes, 10 minutes, 30 minutes, 1 hour, 2 hours, 12 hours or 1 day. The mixing time can be selected by the person skilled in the art according to the equipment and the solids content.

According to one embodiment of the invention, the mixture obtained in step c) is ground during and/or after step c). The milling step may be carried out with any conventional milling device, for example by using a ball mill, centrifugal impact mill, vertical bead mill or attritor, for example. However, any other device capable of milling the mixture obtained in step c) during and/or after method step c) may be used.

The solids content of the mixture obtained in step c) can be adjusted by methods known to the person skilled in the art. To adjust the solids content of the mixture, the suspension may be partially or completely dewatered by filtration, centrifugation or thermal separation methods. Alternatively, water may be added to the mixture until the desired solids content is obtained. According to one embodiment of the invention, the mixture has a solids content of 5-50% by weight, preferably 7-47% by weight and most preferably 9-45% by weight, based on the total weight of the mixture.

Additionally or alternatively, the mixture has a viscosity of 1-1000mPa at 25 DEG CS, more preferably 5-800mPa at 25 DEG CS and most preferably 10-500mPa at 25 DEG CS Brookfield viscosity. According to one embodiment, the brookfield viscosity is measured at 100 rpm.

According to another preferred embodiment of the invention, the mixture obtained in step C) has a temperature of 40-75 ℃, more preferably 45-70 ℃.

According to another preferred embodiment of the invention, the mixture obtained in step c) has a pH value of 7.0 to 13.0, preferably 10.0 to 13.0, more preferably 10.5 to 12.0.

The at least one calcium compound of step a) and the calcium chloride of step b) are mixed in step c) in such an amount that the molar amount of the at least one calcium compound of step a) and the calcium chloride of step b) in the obtained mixture is in the range of 7:93 to 80:20. Preferably, the molar amount of the at least one calcium compound of step a) and the calcium chloride of step b) in the obtained mixture in step c) is in the range of 10:90 to 80:20 (e.g. 15:85 to 80:20), preferably 10:90 to 70:30 (e.g. 15:85 to 70:30), more preferably 15:85 to 50:50 (e.g. 15:85 to 40:60), even more preferably 20:80 to 40:60 and most preferably about 20:80 or about 25:75.

Process step c) may be carried out as a batch process, a semi-continuous process or a continuous process.

Method step d)

In step d) of the present invention, a sodium carbonate source is added to the mixture obtained in step C) at a temperature of 30-70 ℃ and a pH value of 9.5-13.5. The sodium carbonate source is selected from sodium carbonate or a mixture consisting of at least 70% by weight sodium carbonate and at most 30% by weight sodium bicarbonate. Furthermore, the sum of the calcium-containing materials of steps a) and b) and the sodium carbonate source of step d) have a molar ratio of calcium ions to carbonate ions (Ca ²⁺:CO₃ ^2-) in the range of 1.00:1.00 to 1.00:1.30.

In step d) of the present invention, a sodium carbonate source is added to the mixture obtained in step c), wherein the sodium carbonate source is selected from sodium carbonate or a mixture consisting of at least 70% by weight sodium carbonate and at most 30% by weight sodium bicarbonate.

According to one embodiment of the invention, the sodium carbonate source consists of sodium carbonate only. "sodium carbonate" in the meaning of the present invention is a compound having the formula Na ₂CO₃ and consisting of sodium ions and carbonate ions. It is also known as wash alkali, soda ash and soda crystallization.

According to another embodiment of the invention, the sodium carbonate source is a mixture of at least 70% by weight sodium carbonate and at most 30% by weight sodium bicarbonate, based on the total dry weight of the sodium carbonate source. "sodium bicarbonate" in the meaning of the present invention is a compound having the formula NaHCO ₃ and consisting of sodium ions and bicarbonate ions. It is also known as baking soda or sodium bicarbonate. For example, the sodium carbonate source is a mixture consisting of 72.0 to 99.0 weight percent sodium carbonate and 28.0 to 1.0 weight percent sodium bicarbonate, preferably 75.0 to 90.0 weight percent sodium carbonate and 25.0 to 10.0 weight percent sodium bicarbonate, and most preferably 78.0 to 85.0 weight percent sodium carbonate and 22.0 to 15.0 weight percent sodium bicarbonate, based on the total dry weight of the sodium carbonate source.

According to a preferred embodiment of the invention, the sodium carbonate source consists of sodium carbonate only.

The sodium carbonate source may be in a dry form, such as in the form of a powder, or may be in the form of a solution, such as in the form of an aqueous solution. In case the sodium carbonate source is in the form of a solution, the sodium carbonate solution comprises the sodium carbonate source in an amount of 1.0-30% by weight, based on the total weight of the sodium carbonate solution, such as in an amount of 5.0-25% by weight, even more preferably in an amount of 10-20% by weight, such as in an amount of 15% by weight + -2% by weight. Alternatively, the sodium carbonate source is in the form of a solution and comprises the sodium carbonate source in an amount of 1.0-30g/l, such as in an amount of 3.0-25g/l, even more preferably in an amount of 5.0-20g/l, such as in an amount of 15g/l + -2 g/l.

The sodium carbonate source may be added in one portion or in several portions, for example in two, three or four portions. The portions may be the same or different.

According to one embodiment, the sodium carbonate source is added in one portion. For example, the sodium carbonate source consists of sodium carbonate only, preferably in the form of a dry powder, and is added in one portion in step d).

According to another preferred embodiment, the sodium carbonate source is added in two portions. Preferably, the first fraction comprises 0.01 to 5% by weight, more preferably 0.1 to 4.0% by weight, even more preferably 1.0 to 3.0% by weight, and most preferably 1.5 to 2.5% by weight of the total amount of the sodium carbonate source.

Additionally or alternatively, the first part is added in the form of a solution comprising 1.0-30g/l of sodium carbonate source, preferably 3.0-25g/l, even more preferably 5.0-20g/l, even more preferably 7-17g/l and most preferably 8-15g/l of sodium carbonate source.

According to a preferred embodiment, the sodium carbonate source is added in at least two portions, wherein the first portion comprises 0.01-5% by weight, preferably 0.1-4.0% by weight, more preferably 1.0-3.0% by weight and most preferably 1.5-2.5% by weight of the total amount of the sodium carbonate source, and is added in the form of a solution comprising 5-20g/l, preferably 7-17g/l and most preferably 8-15g/l of sodium carbonate source.

The remaining sodium carbonate source may be added after the first part in one part as the second part or in several parts, for example in two, three or four parts. These portions may be the same or different. Additionally or alternatively, the remaining sodium carbonate source may be added after the first portion in solid or solution form, and preferably in solid form.

According to a preferred embodiment, the sodium carbonate source is added to the mixture obtained in step c) in at least two parts, wherein the first part comprises 0.01-5% by weight of the total amount of the sodium carbonate source and is added in the form of a solution comprising 5-20g/l of the sodium carbonate source, preferably wherein the first part of the sodium carbonate source in step d) comprises 0.1-4.0% by weight, more preferably 1.0-3.0% by weight, and most preferably 1.5-2.5% by weight of the total amount of the sodium carbonate source and/or is added in the form of a solution comprising 7-17g/l, preferably 8-15g/l of the sodium carbonate source, and the sodium carbonate source remaining after the first part is added in one part as a second part and the sodium carbonate source remaining after the first part is added as a solid. Preferably, the sodium carbonate source is sodium carbonate.

In step d) of the present invention, a sodium carbonate source is added to the mixture obtained in step C) at a temperature of 30-70 ℃. According to a preferred embodiment, the temperature in step d) is 40-60 ℃, more preferably 45-50 ℃.

It is obvious to a person skilled in the art that the initial temperature of the mixture obtained from step c) is not necessarily the same as the temperature of the mixture prepared in step d). However, if the temperature of the mixture obtained in step C) is below 30 ℃ or above 70 ℃, it must be cooled or heated before the calcium carbonate source in step d) is added. The person skilled in the art knows how to adjust the temperature of the mixture obtained in step c), for example by cooling with a cooling tube or by external heating.

Furthermore, if the sodium carbonate source is added in at least two portions, the temperature at which the first portion is added and the temperature at which the second portion is added may be different or the same, and preferably the same.

According to one embodiment of the invention, the sodium carbonate source is added in step d) in the form of a solution and the temperature of the solution is adjusted to be in the range of more than 10 ℃ and less than 90 ℃. Preferably, the temperature of the sodium carbonate is adjusted to 30 ℃ to 70 ℃, more preferably 40 ℃ to 60 ℃, and most preferably 45 ℃ to 50 ℃.

The person skilled in the art knows how to control the temperature during step d), for example by cooling with a cooling tube or by external heating.

In step d) of the present invention, a sodium carbonate source is added to the mixture obtained in step c) at a pH of 9.5-13.5. According to a preferred embodiment, the pH in step d) is from 10.0 to 13.0, more preferably from 10.5 to 12.0.

It is obvious to a person skilled in the art that the initial pH of the mixture obtained from step c) is not necessarily the same as the pH of the mixture prepared in step d). However, if the pH of the mixture obtained in step c) is below 9.5 or above 13.5, it must be adjusted before the calcium carbonate source in step d) is added. The person skilled in the art knows how to adjust the pH of the mixture obtained in step c), for example by diluting the mixture with water.

Furthermore, if the sodium carbonate source is added in at least two portions, the pH at the time of adding the first portion and the pH at the time of adding the second portion may be different or the same, and preferably the same.

According to one embodiment of the invention, the sodium carbonate source is added in step d) in the form of a solution and the pH of the solution is adjusted to 9.5-13.5, preferably 10.0-13.0, more preferably 10.5-12.0.

The person skilled in the art knows how to control the pH during step d), for example by diluting the mixture with water.

According to a preferred embodiment of the invention, the temperature in step d) is 40-60 ℃, more preferably 45-50 ℃, and the pH is 10.0-13.0, more preferably 10.5-12.0.

The sum of the calcium-containing materials of steps a) and b) and the sodium carbonate source of step d) have a molar ratio of calcium ions to carbonate ions (Ca ²⁺:CO₃ ^2-) of from 1.00:1.00 to 1.00:1.30. Preferably, the sum of the calcium-containing materials of steps a) and b) and the sodium carbonate source of step d) have a molar ratio of calcium ions to carbonate ions (Ca ²⁺:CO₃ ^2-) of from 1.00:1.00 to 1.00:1.20, more preferably from 1.00:1.00 to 1.00:1.10 and most preferably about 1.00:1.05.

More precisely, the molar ratio (Ca ²⁺:CO₃ ^2-) of the total amount of calcium ions of the calcium oxide powder or calcium hydroxide suspension of step a) and the calcium chloride solution of step b) to the total amount of carbonate ions of sodium carbonate or a mixture of sodium carbonate and sodium bicarbonate is 1.00:1.00 to 1.00:1.30, preferably 1.00:1.00 to 1.00:1.20, more preferably 1.00:1.00 to 1.00:1.10 and most preferably about 1.00:1.05.

The inventors have unexpectedly found that by the above process it is possible to control the morphology of the precipitated calcium carbonate and obtain a scalenohedral PCC product.

According to one embodiment of the invention, the scalenohedral PCC product obtained in step d) has a specific surface area of 0.1-25.0m ²/g, preferably 0.5-20.0m ²/g and most preferably 1.0-15.0m ²/g, measured according to ISO 9277:2010 using nitrogen and BET methods.

Additionally or alternatively, the scalenohedral PCC product obtained in step d) is in the form of particles having a volume-based median particle size d ₅₀ (vol) of from 0.05 to 10 μm, preferably from 0.2 to 8 μm, more preferably from 0.4 to 5 μm and most preferably from 1.0 to 3.5 μm.

Additionally or alternatively, the scalenohedral PCC product obtained in step d) is in the form of particles having a volume-based undercut particle size d ₉₈ (vol) of 0.15-20 μm, preferably 1-15 μm, more preferably 1.5-10 μm and most preferably 2-8 μm.

Additionally or alternatively, the scalenohedral PCC product obtained in step d) has an ISO whiteness (R457) measured according to ISO 2469:2014 of at least 90%, preferably at least 92%, more preferably at least 9% and most preferably at least 97%.

Additionally or alternatively, the scalenohedral PCC product obtained in step d) has a Yellowness Index (YI) measured according to DIN 6167 of below 2, preferably below 1.8, more preferably below 1.6 and most preferably between 0.5 and 1.5.

Additionally or alternatively, the scalenohedral PCC product obtained in step d) comprises at least 80% by weight, preferably 90% by weight and most preferably 95% by weight scalenohedral PCC based on the total dry weight of the scalenohedral PCC product. The scalenohedral (PCC) precipitated calcium carbonate according to the present invention is in the form of calcite, which has a trigonal structure with scalenohedral crystal habit. Scalenohedral PCC exhibits triangular clusters of crystals (rosettes) emanating from a central core.

Additionally or alternatively, the scalenohedral PCC product obtained in step d) comprises 20% by weight or less, preferably 10% by weight or less and most preferably 5% by weight or less of aragonite based on the total dry weight of the scalenohedral PCC product. Aragonite within the meaning of the present invention is an orthorhombic structure having the typical crystal habit of paired hexagonal prisms, as well as a variety of classifications of elongated prismatic, curved leaf-like, steep taper, chisel-tipped, bifurcated tree, and coral or worm-like forms.

According to another embodiment, the scalenohedral PCC product obtained in step d) comprises at least 80 wt. -%, preferably 90 wt. -% and most preferably 95 wt. -% scalenohedral PCC based on the total dry weight of the scalenohedral PCC product and 20 wt. -% or less, preferably 10 wt. -% or less and most preferably 5 wt. -% or less aragonite based on the total dry weight of the scalenohedral PCC product. According to a preferred embodiment of the present invention, the scalenohedral PCC product obtained in step d) consists of scalenohedral (PCC) precipitated calcium carbonate only.

According to one embodiment of the invention, the scalenohedral PCC product obtained

According to a more specific embodiment of the present invention, the scalenohedral PCC product obtained has an ISO whiteness (R457) of at least 90%, preferably at least 92%, more preferably at least 95% and most preferably at least 97%, and a Yellowness Index (YI) of less than 2, preferably less than 1.8, more preferably less than 1.6 and most preferably from 0.5 to 1.5.

According to a more specific embodiment of the present invention, the scalenohedral PCC product obtained

-Having a specific surface area of 0.1-25.0m ²/g, preferably 0.5-20.0m ²/g and most preferably 1.0-15.0m ²/g, measured according to ISO 9277:2010 using nitrogen and BET methods, and

In the form of particles having a volume-based median particle size d ₅₀ (vol) of 0.05 to 10 μm, preferably 0.2 to 8 μm, more preferably 0.4 to 5 μm and most preferably 1.0 to 3.5 μm, and

-Having an ISO whiteness (R457) of at least 90%, preferably at least 92%, more preferably at least 95% and most preferably at least 97%, and

-A Yellowness Index (YI) of less than 2, preferably less than 1.8, more preferably less than 1.6 and most preferably 0.5-1.5.

As described above, the present inventors have unexpectedly found that by the above process it is possible to control the morphology of precipitated calcium carbonate and obtain a scalenohedral PCC product.

Furthermore, the inventors have found that calcium chloride can be used as an additional calcium source in addition to calcium oxide or lime milk.

Additionally, the inventors have unexpectedly found that no carbon dioxide containing compound, in particular no gaseous carbon dioxide, is required to obtain a scalenohedral PCC product in the process of the present invention. Instead, a sodium carbonate source selected from sodium carbonate or a mixture consisting of at least 70% by weight sodium carbonate and at most 30% by weight sodium bicarbonate is sufficient to produce a scalenohedral PCC product at the temperatures and pH values described above.

The process for producing these particles is an easy and quick process and the product obtained is affordable and particularly easy to handle. The method can be performed in standard equipment without imposing significant burden on humans and the environment. Furthermore, the inventive process has a reduced carbon dioxide footprint and is inexpensive, easy to handle and easy to adjust to accommodate. Additionally, no chemicals are used in the method of the present invention that are toxic or harmful to the user. In addition, the by-products obtained in this process are also non-toxic or harmless and can even be recovered for subsequent use, for example sodium chloride.

Additional method steps

The method of the invention may comprise additional method steps.

According to another embodiment of the invention, the method further comprises a step e) of adding an additive to the mixture obtained in step c).

According to one embodiment, the additive added in step d) is a dispersant.

Conventional dispersants known to those skilled in the art may be used. One skilled in the art will select the dispersant based on its equipment and the intended use of the scalenohedral PCC.

Suitable dispersants may be selected from polyphosphates, and in particular tripolyphosphates. Another suitable dispersant may be selected from homopolymers or copolymers based on, for example, polycarboxylates of acrylic acid, methacrylic acid, maleic acid, fumaric acid or itaconic acid, and acrylamide, or mixtures thereof. The homopolymer or copolymer of the polycarboxylate may be fully or partially neutralized, e.g., at least 70%, or at least 80%, or at least 90% of the acid groups are neutralized. Neutralization means that the protons of the carboxylic acid are exchanged with another cation, such as sodium and/or calcium cations. According to a preferred embodiment, the homopolymer or copolymer of the polycarboxylate is fully neutralized and most preferably with sodium and/or calcium ions. Homopolymers or copolymers of acrylic acid are particularly preferred. Most preferred are homopolymers or copolymers of acrylic acid that are fully neutralized with sodium and/or calcium ions. The weight average molecular weight M _w of such products is preferably in the range from 2 000 to 15 g/mol, with a weight average molecular weight M _w of from 3 000 to 7 g/mol or from 3 500 to 6 g/mol being particularly preferred. According to an exemplary embodiment, the dispersant is sodium polyacrylate having a weight average molecular weight M _w of 2 000-15 g/mol, preferably 3-7 g/mol and most preferably 3-500 g/mol.

According to one embodiment, the additive added in step d) is a nucleating agent.

Conventional nucleating agents known to those skilled in the art may be used. One skilled in the art will select a nucleating agent based on its equipment and the intended use of the scalenohedral PCC.

Suitable nucleating agents may be selected from sucrose, sugar alcohols, citrate or citric acid and most preferably may be sucrose.

According to one embodiment of the invention, the method further comprises a step e) of adding additives, preferably dispersants and/or nucleating agents, such as sucrose or citrate and most preferably sucrose, to the mixture obtained in step c).

According to a preferred embodiment, the scalenohedral PCC product is separated from the obtained suspension, for example by filtration. A dispersant, preferably in the form of a solution or dispersion, may then be added to the filter cake. Those skilled in the art will know how to filter and redisperse the scalenohedral PCC product and will choose the dispersant and separation method depending on its equipment and intended use.

The aqueous suspension obtained after step d) may be further processed, e.g. the scalenohedral PCC product may be separated from the aqueous suspension and/or subjected to a drying step.

According to one embodiment, the process of the present invention further comprises a step f) of separating the scalenohedral PCC product from the aqueous suspension obtained in step d). Thus, a method for producing a scalenohedral PCC product may comprise the steps of:

Wherein the sum of the calcium-containing materials of steps a) and b) and the sodium carbonate source of step d) have a molar ratio of calcium ions to carbonate ions (Ca ²⁺:CO₃ ^2-) of from 1.00:1.00 to 1.00:1.30, and

E) Separating the scalenohedral PCC product from the aqueous suspension obtained in step d).

The scalenohedral PCC product obtained from step d) may be separated from the aqueous suspension by any conventional separation means known to the person skilled in the art. According to one embodiment of the invention, in process step e), the scalenohedral PCC product is mechanically and/or thermally separated. Examples of mechanical separation processes are filtration, for example by means of rotary drum filters or filter presses, nanofiltration or centrifugation. An example of a thermal separation process is a concentration process by applying heat, for example in an evaporator. According to a preferred embodiment, in process step e), the scalenohedral PCC product is isolated by solvent evaporation and/or pressure filtration.

After separation, the scalenohedral PCC product may be dried to obtain a dried scalenohedral PCC product. According to one embodiment, the process of the present invention further comprises step f) after step d) or after step e) (if present), drying the scalenohedral PCC product at a temperature of 60-120 ℃, preferably 80-110 ℃ and most preferably 95-105 ℃, preferably until the moisture content of the scalenohedral PCC product is less than 1% by weight, based on the total weight of the dried scalenohedral PCC product. Thus, a method for producing a scalenohedral PCC product may comprise the steps of:

E) Separating the scalenohedral PCC product from the aqueous suspension obtained in step d), and

F) Drying the scalenohedral PCC product.

In general, the drying step f) may be performed using any suitable drying apparatus and may for example comprise thermal drying and/or reduced pressure drying, using apparatus such as an evaporator, flash dryer, oven, spray dryer, and/or drying in a vacuum chamber. The drying step f) may be carried out under reduced pressure, ambient pressure or increased pressure. For temperatures below 100 ℃, it may be preferred to carry out the drying step under reduced pressure. The drying step may be performed for at least 30 seconds, at least 1 minute, 2 minutes, 5 minutes, 10 minutes, 30 minutes, 1 hour, 2 hours, 12 hours, or 1 day, for example. The drying time can be selected by one skilled in the art depending on the equipment, water content and intended use.

According to one embodiment, in process step f), the scalenohedral PCC product is dried until the moisture content of the scalenohedral PCC product is less than or equal to 1.0 wt. -%, preferably less than or equal to 0.5 wt. -%, and more preferably less than or equal to 0.2 wt. -%, based on the total weight of the dried scalenohedral PCC product.

According to another embodiment, the process according to the invention further comprises a step g) of treating the surface of the scalenohedral PCC product obtained in step d) and/or step e) and/or step f). Thus, a method for producing a scalenohedral PCC product may comprise the steps of:

F) Drying the scalenohedral PCC product, and

G) The surface of the resulting scalenohedral PCC product is treated.

In general, the treatment step g) may be carried out using any suitable treatment agent, for example a hydrophobic agent such as a fatty acid. Such hydrophobizing agents as stearic acid and palmitic acid are known to those skilled in the art and are commercially available. Surface treatment of scalenohedral PCC products may affect the rheological properties of the material.

The process of the present invention may be carried out as a batch process, a semi-continuous process or a continuous process. According to a preferred embodiment of the invention, the process according to the invention is carried out as a batch process.

According to an exemplary embodiment of the present invention, a method for producing a scalenohedral PCC product may include the steps of:

a) Providing at least one calcium compound which is a suspension of calcium hydroxide and has a solids content of 5-50% by weight, preferably 9-45% by weight, and the calcium hydroxide particles have a volume median particle size d ₅₀ (vol) of 0.05-25 μm, preferably 1.0-3.5 μm;

b) Providing a calcium chloride solution, wherein the solution comprises 0.5-270g/l, preferably 5.0-50g/l of calcium;

d) Adding a sodium carbonate source to the mixture obtained in step C) at a temperature of 30-70 ℃ and at a pH value of 9.5-13.5, the sodium carbonate source is sodium carbonate and the sodium carbonate source is sodium carbonate,

E) Optionally separating the scalenohedral PCC product from the aqueous suspension obtained in step d), and

F) Optionally, drying the scalenohedral PCC product.

According to another exemplary embodiment of the present invention, a method for producing a scalenohedral PCC product may include the steps of:

d) Adding a sodium carbonate source to the mixture obtained in step C) at a temperature of 30-70 ℃ and at a pH value of 9.5-13.5, the sodium carbonate source is a sodium carbonate solution,

F) Optionally, drying the scalenohedral PCC product.

According to an exemplary embodiment, a sodium carbonate source is added to the mixture obtained in step c) in at least two portions,

Wherein the first part comprises 0.01-5% by weight of the total amount of the sodium carbonate source and is added in the form of a solution comprising 5-20g/l sodium carbonate source, preferably 1.0-3.0% by weight and is added in the form of a solution comprising 8-15g/l sodium carbonate source, the sodium carbonate source remaining after the first part is added as a second part and is also in the form of a solution.

According to another exemplary embodiment of the present invention, a method for producing a scalenohedral PCC product may comprise the steps of:

d) Adding a sodium carbonate source to the mixture obtained in step C) at a temperature of 30-70 ℃ and at a pH value of 9.5-13.5, the sodium carbonate source being a mixture consisting of at least 70% by weight sodium carbonate and at most 30% by weight sodium bicarbonate,

F) Optionally, drying the scalenohedral PCC product.

Product and use thereof

According to one embodiment of the present invention, there is provided a scalenohedral PCC product obtained by a process comprising the steps of:

Furthermore, the method may comprise a step e) of adding additives, preferably dispersants and/or nucleating agents, such as sucrose or citrate, and most preferably sucrose, to the mixture obtained in step c).

Furthermore, the process may comprise a step f) of separating the scalenohedral PCC product from the aqueous suspension obtained in step d), and preferably, step f) is performed by solvent evaporation and/or pressure filtration, and/or step g) of drying the scalenohedral PCC product after step d) or after step f), if present, at a temperature of 60-120 ℃, preferably 80-110 ℃ and most preferably 95-105 ℃, preferably until the moisture content of the scalenohedral PCC product is less than 1% by weight, based on the total weight of the dried scalenohedral PCC product.

Scalenohedral PCC products are obtained by the process of the present invention. According to a preferred embodiment, the obtained scalenohedral PCC product comprises at least 80% by weight, preferably 90% by weight and most preferably 95% by weight scalenohedral PCC based on the total dry weight of the scalenohedral PCC product. The scalenohedral (PCC) precipitated calcium carbonate according to the present invention is in the form of calcite, which has a trigonal structure with scalenohedral crystal habit. Scalenohedral PCC exhibits triangular clusters of crystals (rosettes) emanating from a central core.

According to another preferred embodiment, the resulting scalenohedral PCC product comprises 20% by weight or less, preferably 10% by weight or less and most preferably 5% by weight or less of aragonite, based on the total dry weight of the scalenohedral PCC product. Aragonite within the meaning of the present invention is an orthorhombic structure having the typical crystal habit of paired hexagonal prisms, as well as a variety of classifications of elongated prismatic, curved leaf-like, steep taper, chisel-tipped, bifurcated tree, and coral or worm-like forms.

According to a preferred embodiment of the present invention, the obtained scalenohedral PCC product comprises at least 80 wt. -%, preferably 90 wt. -% and most preferably 95 wt. -% scalenohedral PCC based on the total dry weight of the scalenohedral PCC product and 20 wt. -% or less, preferably 10 wt. -% or less and most preferably 5 wt. -% or less aragonite based on the total dry weight of the scalenohedral PCC product.

According to one embodiment of the present invention, the scalenohedral PCC product obtained consists solely of scalenohedral (PCC) precipitated calcium carbonate.

According to another embodiment of the present invention, the scalenohedral PCC product obtained in step d) has an ISO whiteness (R457) measured according to ISO 2469:2014 of at least 90%, preferably at least 92%, more preferably at least 9% and most preferably at least 97%.

According to another embodiment of the present invention, the scalenohedral PCC product obtained in step d) has a Yellowness Index (YI) measured according to DIN 6167 of less than 2, preferably less than 1.8, more preferably less than 1.6 and most preferably between 0.5 and 1.5.

According to a preferred embodiment of the present invention, the scalenohedral PCC product obtained

According to another preferred embodiment of the present invention, the scalenohedral PCC product obtained

I) Has a specific surface area of 0.1 to 25.0m ²/g, preferably 0.5 to 20.0m ²/g and most preferably 1.0 to 15.0m ²/g, measured according to ISO 9277:2010 using nitrogen and BET methods, and

Ii) is in the form of particles having a volume-based median particle size d ₅₀ (vol) of from 0.05 to 10 μm, preferably from 0.2 to 8 μm, more preferably from 0.4 to 5 μm and most preferably from 1.0 to 3.5 μm, and

According to a more specific embodiment of the present invention, the scalenohedral PCC product obtained has an ISO whiteness (R457) of at least 90%, preferably at least 92%, more preferably at least 95% and most preferably at least 97%, and a Yellowness Index (YI) of less than 2, preferably less than 1.8, more preferably less than 1.6 and most preferably between 0.5 and 1.5.

The inventors of the present invention have surprisingly found that the precipitated calcium carbonate product obtained by the process of the present invention has improved properties. More precisely, the precipitated calcium carbonate product has a controlled morphology, i.e. the obtained precipitated calcium carbonate product is a scalenohedral PCC product. Furthermore, in the inventive process according to the present invention, no carbon dioxide containing compounds, in particular no gaseous carbon dioxide, are required, and thus the resulting scalenohedral PCC product has a reduced carbon dioxide footprint, which is becoming increasingly important today. Furthermore, the process of the present invention is very economical and ecological. Furthermore, in this method, no chemicals that are toxic or harmful to the user are used. Moreover, the by-products obtained in the process are also non-toxic or harmless and can even be recovered for subsequent use, for example sodium chloride.

The inventors have unexpectedly found that the scalenohedral PCC product obtained by the process of the present invention can be used in polymer applications, paper coating applications, papermaking, paints, coatings, sealants, adhesives, feeds, pharmaceuticals, concrete, cements, cosmetics, water treatment, engineered wood applications, gypsum board applications, packaging applications, catalysis, gas treatment applications and/or agricultural applications. It is particularly advantageous to use the scalenohedral PCC product obtained by the process of the present invention in the field where a defined morphology of the filler or pigment is required.

Drawings

Fig. 1 is an SEM photograph of example 1, showing the morphology of the resulting precipitated calcium carbonate product obtained by the comparative method.

Fig. 2 is an SEM photograph of example 2 showing the morphology of the resulting precipitated calcium carbonate product obtained by the process of the present invention.

Fig. 3 is an SEM photograph of example 3 showing the morphology of the resulting precipitated calcium carbonate product obtained by the process of the present invention.

Fig. 4 is an SEM photograph of example 4 showing the morphology of the resulting precipitated calcium carbonate product obtained by the process of the present invention.

Fig. 5 is an SEM image of the product obtained by example 5, showing PCC crystals having scalenohedral morphology.

Fig. 6 is an SEM image of the product obtained by example 6, showing PCC crystals having scalenohedral morphology.

Fig. 7 is an SEM image of the product obtained by example 7, showing PCC crystals having scalenohedral morphology.

Fig. 8 is an SEM image of the product obtained by example 8, showing PCC crystals having scalenohedral morphology.

Fig. 9 is an SEM image of the product obtained by example 9, showing PCC crystals having scalenohedral morphology.

Fig. 10 is an SEM image of the product obtained by reference example 1.

Fig. 11A and 11B show SEM images of two different magnifications of the product obtained by reference example 2.

Detailed Description

The scope and benefits of the present invention will be better understood based on the following non-limiting examples, which are intended to illustrate certain embodiments of the present invention.

Examples

1. Measurement method

Particle size distribution

The volume median particle diameter was determined by laser diffraction. This method is based on the deflection of the laser beam by particles dispersed in a liquid or air stream as a whole. Diffraction or scattering angles are characteristic of particle size. Volume-based median particle size d ₅₀ (vol) and particle size d ₉₀ (vol) and volume-based undercut particle size d ₉₈ (vol) were evaluated using a HELOS particle size analyzer and software windows of Sympatec GmbH. The value d ₅₀ (vol) or d ₉₀ (vol) or d ₉₈ (vol) represents a diameter value such that 50%, 90% or 98% by volume of the particles, respectively, have a diameter smaller than this value. Raw data obtained by measurement were analyzed using the Mie (Mie) theory, in which the refractive index of particles is 1.57 and the absorption index is 0.005. Methods and apparatus are known to those skilled in the art and are commonly used to determine particle size distribution of fillers and pigments. The particle size of the obtained scalenohedral PCC product was measured in water, and the particle size of calcium hydroxide was measured in analytically pure ethanol.

The weight median particle diameter d ₅₀ (wt) and the weight-based particle size d ₉₀ (wt) are determined by sedimentation, which is an analysis of the sedimentation behavior in a gravitational field. Measurements were made using a Micromeritics Instrument Corporation Sedigraph ^TM 5120. Methods and instruments are known to those skilled in the art and are commonly used to determine the particle size of fillers and pigments. Measurements were made in an aqueous solution of 0.1% by weight Na ₄P₂O₇. Dispersing samples using high speed agitators and sonication

Methods and instruments are known to those skilled in the art and are commonly used to determine the particle size of fillers and pigments.

X-ray diffraction (XRD)

XRD experiments were performed on samples using a rotatable PMMA support ring. Samples were analyzed using a Bruker D8 Advance powder diffractometer following Bragg's law. The diffractometer consisted of a 2.2 kW X tube, sample holder, theta-theta goniometer and V a NTEC-1 detector. Nickel filtered Cu-K alpha radiation was used in all experiments. The profile is a graph automatically recorded in 2 theta using a scan rate of 0.7 deg. per minute. Using DIFFRACsuite software packages EVA and SEARCH, the resulting powder diffraction patterns can be easily classified by mineral content based on the reference patterns of the ICDD PDF 2 database.

Quantitative analysis of diffraction data refers to determining the amount of different phases in a multiphase sample and has been performed using DIFFRACsuite software package TOP AS. In detail, quantitative analysis allows structural properties and phase ratios to be determined using quantifiable digital precision from the experimental data itself. This involves modeling of the full diffraction pattern (using the Rietveld method) so that the calculated pattern replicates what is obtained from the experiment.

BET Specific Surface Area (SSA)

After conditioning the samples by heating at 250 ℃ for a period of 30 minutes, the specific surface area was measured by BET method using nitrogen according to ISO 9277:2010. Prior to this measurement, the samples were filtered in a buchner funnel, rinsed with deionized water and dried in an oven at 90-100 ℃ overnight. Subsequently, the dry cake was sufficiently ground in a mortar, and the resulting powder was placed in a moisture balance (moistureproof balance) at 130 ℃ until a constant weight was reached.

Viscosity measurement

Brookfield DV-II+Pro viscometer was used to measure Brookfield viscosity at 25.+ -. 1 ℃ using a suitable rotor of the Brookfield RV-rotor set, and specified as mPa, at 100 rpmS. A rotor suitable for the viscosity range to be measured is selected from the Brookfield RV-rotor set. For <200mPaS, using rotor number 2, for a viscosity range of 200-800mPaViscosity range between s, rotor number 3 was used for a viscosity range between 400 and 1600mPaViscosity range between s, rotor number 4 was used, and for 800-3200mPaThe viscosity range between s, rotor number 5 was used.

Suspension/solution pH measurement

The pH of the suspension or solution was measured at 25℃using a Mettler-Toledo SEVEN EASY PH meter and a Mettler-Toledo InLab ^® Expert Pro pH electrode.

Three-point calibration of the instrument (according to the segmentation method) was first performed using commercially available buffer solutions (from Aldrich) with pH values of 4, 7 and 10 at 20 ℃.

The reported pH is the end point value of the instrument detection (end point is the point when the difference between the measured signal and the average value over the last 6 seconds is less than 0.1 mV).

Suspension/solution conductivity measurement

The conductivity of the suspension was measured at 25 ℃ immediately after stirring the suspension at 1500rpm using a pendragik fluted disc stirrer using Mettler Toledo Seven Multi equipped with a corresponding Mettler Toledo conductivity expansion unit and Mettler Toledo InLab ^® conductivity probes.

The instrument was first calibrated using a commercially available conductivity calibration solution (from Mettler Toledo) over the relevant conductivity range. The effect of temperature on conductivity is automatically corrected by a linear correction mode.

The measured conductivity is reported as a reference temperature of 20 ℃. The conductivity values reported are the endpoint values detected by the instrument (endpoint when the measured conductivity differs by less than 0.4% from the average value over the last 6 seconds).

Moisture content measurement

The obtained samples were measured at t=160 ℃ using Halogen Moisture Analyzer HR73 of Mettler-Toledo. The moisture content of the samples was measured by measuring the weight of the samples (5-20 g) and then rapidly heating the samples by an integral halogen dryer unit. During heating, the moisture evaporates and the instrument continuously measures the weight of the sample and indicates the moisture loss. At the completion of the drying, the moisture content of the sample was shown as a final result when the weight of the sample was no longer changed.

Whiteness measurement and yellowness index

Pigment whiteness and Yellowness Index (YI) of the obtained particles were measured according to ISO 2469:2014 and DIN 6167, respectively, using ELREPHO 45 OX from Datacolor company. The values obtained are recorded as ISO whiteness R457 (%)

The sample was dried in an oven at 105 ℃ to a residual moisture content <0.5% by weight and the resulting powder was treated to deagglomerate the powder particles. Lozenges were pressed from 12g of the powder via application of 4 bar pressure for 15 seconds. The resulting powder tablets with a diameter of 45 mm were then measured.

In this measurement, the yellowness index is measured via the reflectance of the precipitated calcium carbonate product obtained by the measurement, with an illuminant of D65 and a standard observer function of 10 °.

The yellowness index according to DIN 6167 is calculated as follows:

Wherein X, Y and Z are CIE tristimulus values (Tristimulus value), and these coefficients depend on the illuminant and observer functions indicated in the following table:

2. Examples

Materials and apparatus used

The calcium chloride solutions of examples 1-4 (CaCl ₂) were obtained from Solvay and had sheds mass% of 77-80%

Examples 5-9 calcium chloride solution (CaCl ₂) saline solution (Ca ²⁺ concentration about 42 g/L) containing CaCl ₂ obtained from (aqueous phosphor) recycling process

Sodium carbonate (Na ₂CO₃) available from Solvay under the trade name Soda Solvay Light

Calcium oxide (CaO) is available from Polish lime quarry Lhoist Bukowa

Example 1 comparative example

This comparative example discloses a process for producing Precipitated Calcium Carbonate (PCC) from a brine solution comprising calcium chloride (CaCl ₂). The process involves the reaction of calcium chloride with sodium carbonate, which produces precipitated calcium carbonate.

The process for precipitating calcium carbonate was carried out in a cylindrical stainless steel reactor with a double jacket, the capacity of which was 1000 liters. The reactor was equipped with a high shear impeller powered by a 55kW motor operating at 1480 rpm and utilizing stator rotor principles. In addition, pH and conductivity probes were installed in the reactor to monitor the suspension throughout the process.

400 Liters of CaCl ₂ -containing solution/brine were obtained, characterized in that the dissolved Ca ²⁺ concentration was 42g/l. This solution/brine was transferred to a high shear reactor. The temperature of the reaction mixture was adjusted to 50 ℃.

During the initial nucleation stage of the reaction, 1100g/min sodium carbonate powder (Na ₂CO₃) was added to the mixture. This process was carried out in a high shear reactor with vigorous stirring for 40 minutes. The addition is then stopped. This means that a total mass of 44kg of dry Na ₂CO₃ was added to the mixture, which corresponds to a 1:1 stoichiometric ratio between calcium ions (Ca ²⁺) and carbonate ions (CO ₃ ^2-).

The resulting suspension of structured precipitated CaCO ₃ is dewatered and brine mother liquor is exchanged with fresh water on a wash filter known to those skilled in the art, such as a vacuum spin filter or belt filter having a wash zone.

The washed filter cake was redispersed with fresh water to obtain an aqueous slurry of structured precipitated CaCO ₃ having a solids content of 17%, a conductivity of about 299 μs/cm and a pH (25 ℃) of 10.5.

Optionally, the PCC slurry may be dried on a spray dryer to obtain a structured precipitated CaCO ₃ powder with about 0.2% residual moisture.

Example 2-example of the invention

The following exemplary examples of the present invention relate to the preparation of scalenohedral precipitated calcium carbonate from a brine solution comprising calcium chloride (CaCl ₂). The process involves reacting calcium chloride and calcium hydroxide with Na ₂CO₃ to form precipitated calcium carbonate. Example 2 was performed in a similar manner to example 1, except that calcium hydroxide was added to the brine solution prior to the addition of Na ₂CO₃.

Preparing calcium hydroxide slurry. 7.8kg of quick lime (CaO) from Polish was added to 62 liters of tap water in a stirred reactor. The water temperature was adjusted to 50 ℃ prior to adding the quicklime. The digestion process was carried out under continuous stirring for 40 minutes. The resulting slurry (called "milk of lime") was screened through a 100 μm screen. The solids content of the digested milk of lime was 14.7% w/w.

To produce a milk of lime having a particle size d ₅₀ (vol) of 2.5 μm, the milk of lime from the previous step is wet-milled in a stirred bead mill with a specific energy input of about 30 kWh/DTO. The resulting milk of lime was screened through a 45 μm mesh size to remove any larger particles. Particle size d ₅₀ (vol) was measured with Helos Sympatec using ethanol.

To initiate the process, 400 liters of brine solution containing CaCl ₂ was transferred to a high shear reactor. The solution had a dissolved Ca ²⁺ concentration of 42g/l. To this solution 72kg of produced milk of lime was added with stirring in an amount corresponding to 25% Ca ²⁺ from Ca (OH) ₂ seeds and 75% Ca ²⁺ from dissolved CaCl ₂ in brine. Next, 31g of sucrose was added to the reaction mixture with stirring, which corresponds to 0.1% dry sucrose to dry CaO in the mixture. The temperature of the mixture was adjusted to about 50 ℃.

In the initial stage of the reaction, 1466g/min sodium carbonate powder (Na ₂CO₃) was added to the mixture. This process was carried out in a high shear reactor with vigorous stirring for 40 minutes. The addition is then stopped. This means that a total mass of 58.6kg of dry Na ₂CO₃ was added to the mixture, which corresponds to a 1:1 stoichiometric ratio between calcium ions (Ca ²⁺) and carbonate ions (CO ₃ ^2-).

The dehydration, washing, redispersion and characterization of the precipitated calcium carbonate obtained were carried out as described in example 1 above.

Example 3 example of the invention

Example 3 was performed in a similar manner to example 2, except that sodium carbonate (Na ₂CO₃) was dosed in liquid form rather than in dry powder form within 20 minutes.

11.6L/min of aqueous Na ₂CO₃ as a first portion, which has been highly diluted to 1% w/w and adjusted to a temperature of about 50 ℃, was continuously added to the reaction mixture under vigorous stirring in a high shear reactor. The addition was stopped after 5 minutes, which corresponds to a total volume of 58 liters of aqueous Na ₂CO₃ solution and corresponds to 1% by weight of the total amount of sodium carbonate.

Subsequently, 22.4l/min of an aqueous Na ₂CO₃ solution, which had been diluted to 15% w/w and adjusted to a temperature of about 50 ℃, was continuously added as a second portion to the reaction mixture under vigorous stirring in a high-shear reactor. The addition was stopped after 15 minutes, which corresponds to a total volume of 336.6 liters of aqueous Na ₂CO₃ solution and corresponds to 99% by weight of the total sodium carbonate. Total Na ₂CO₃ corresponds to a 1:1 stoichiometric ratio between calcium ions (Ca ²⁺) and carbonate ions (CO ₃ ^2-).

Example 4-example of the invention

Example 4 was performed in a similar manner to example 2, except that sodium carbonate powder (Na ₂CO₃) was dosed as a mixture with sodium bicarbonate powder (NaHCO ₃).

1638G/min of a homogeneous mixture comprising 80% by weight sodium carbonate powder (Na ₂CO₃) and 20% by weight sodium bicarbonate powder was added to the reaction mixture. This process was carried out in a high shear reactor with vigorous stirring for 40 minutes. The addition is then stopped. This means that dry Na ₂CO₃ with a total mass of 65.5kg was added to the mixture, which corresponds to a 1:1 stoichiometric ratio between calcium ions (Ca ²⁺) and carbonate ions (CO ₃ ^2-), and the addition was stopped.

Example 5 example of the invention

Calcium hydroxide slurry ("lime cream") was prepared by adding 500g of quicklime (CaO) from the polish Bukowa to about 4 liters of tap water in a stirred reactor. The resulting slurry was screened through a 100 μm screen. To produce a milk of lime having a particle size d ₅₀ (vol) of about 1 μm, the milk of lime from the previous step is wet-milled in a stirred bead mill (Dynomill with Cermil 0.45.45 mm milling media) having a volume flow of 30L/h. The lime milk obtained was screened through a 45 μm mesh size. Particle size d ₅₀ (vol) was measured with Helos Sympatec using ethanol.

To initiate the process, 6 liters of brine solution (obtained from an aqueous phosphor recycling process) containing CaCl ₂ was transferred to a high shear reactor. 875g of produced lime milk was added to the solution with stirring in an amount corresponding to 20% of Ca ²⁺ from lime milk (Ca (OH) ₂) and 80% of Ca ²⁺ from dissolved CaCl ₂ in brine (total Ca ²⁺ concentration after addition of lime milk: 38.2 g/L). Next, 0.44g of sucrose was added to the reaction mixture with stirring, which corresponds to 0.1% dry sucrose to dry CaO in the mixture. The temperature of the mixture was adjusted to about 50 ℃.

In the initial stage of the reaction, 41g/min sodium carbonate powder (Na ₂CO₃) was added to the mixture. This process was carried out in a high shear reactor with vigorous stirring for 20 minutes. The addition is then stopped. This means that dry Na ₂CO₃ with a total mass of 825g was added to the mixture, which corresponds to a 1:1 stoichiometric ratio between calcium ions (Ca ²⁺) and carbonate ions (CO ₃ ^2-).

The resulting suspension of structured precipitated CaCO ₃ is dewatered and brine mother liquor is exchanged with fresh water on a wash filter known to those skilled in the art, such as a vacuum spin filter or belt filter having a wash zone. The washed filter cake is redispersed with fresh water to obtain an aqueous slurry of structured precipitated CaCO ₃ having a conductivity of less than 500 μS/cm.

Example 6 example of the invention

Example 6 was performed in a similar manner to example 5, except that sodium carbonate powder (Na ₂CO₃) was dosed for 23 minutes to provide a total mass of 948g of dry Na ₂CO₃, which corresponds to a stoichiometric ratio of 1:1.15 between calcium ions (Ca ²⁺) and carbonate ions (CO ₃ ^2-).

Example 7 example of the invention

Example 7 was performed in a similar manner to example 5, except that sodium carbonate powder (Na ₂CO₃) was dosed for 26 minutes to provide a total mass of 1072g of dried Na ₂CO₃, which corresponds to a 1:1.3 stoichiometric ratio between calcium ions (Ca ²⁺) and carbonate ions (CO ₃ ^2-).

Example 8 example of the invention

Calcium hydroxide slurry ("lime cream") was prepared by adding 2000g of quicklime (CaO) from poland Bukowa to about 16 liters of tap water in a stirred reactor. The resulting slurry was screened through a 100 μm screen. To produce a milk of lime having a particle size d ₅₀ (vol) of about 1 μm, the milk of lime from the previous step is wet-milled in a stirred bead mill (Dynomill with Cermil 0.45.45 mm milling media) having a volume flow of 30L/h. The lime milk obtained was screened through a 45 μm mesh size. Particle size d ₅₀ (vol) was measured with Helos Sympatec using ethanol.

To initiate the process, 3 liters of brine solution (obtained from an aqueous phosphor recycling process) containing CaCl ₂ was transferred to a high shear reactor. 3370g of the produced milk of lime was added to the solution with stirring in an amount corresponding to 67% of Ca ²⁺ from milk of lime (Ca (OH) ₂) and 33% of Ca ²⁺ from dissolved CaCl ₂ in brine (total Ca ²⁺ concentration after addition of milk of lime: 64.3 g/L). Next, 0.53g of sucrose was added to the reaction mixture with stirring, which corresponds to 0.1% dry sucrose to dry CaO in the mixture. The temperature of the mixture was adjusted to about 50 ℃.

In the initial stage of the reaction, 50g/min sodium carbonate powder (Na ₂CO₃) was added to the mixture. This process was carried out in a high shear reactor with vigorous stirring for 20 minutes. The addition is then stopped. This means that 1000g of dry Na ₂CO₃ was added to the mixture, which corresponds to a 1:1 stoichiometric ratio between calcium ions (Ca ²⁺) and carbonate ions (CO ₃ ^2-).

Example 9 example of the invention

Example 9 was performed using the same milk of lime as described in example 8.

To initiate the process, 3 liters of brine solution (obtained from an aqueous phosphor recycling process) containing CaCl ₂ was transferred to a high shear reactor. 6988g of produced lime milk was added to the solution with stirring in an amount corresponding to 80% of Ca ²⁺ from lime milk (Ca (OH) ₂) and 20% of Ca ²⁺ from dissolved CaCl ₂ in brine (total Ca ²⁺ concentration after addition of lime milk: 127.3 g/L). Next, 0.87g sucrose was added to the reaction mixture with stirring, which corresponds to 0.1% dry sucrose to dry CaO in the mixture. The temperature of the mixture was adjusted to about 50 ℃.

In the initial stage of the reaction, 83g/min sodium carbonate powder (Na ₂CO₃) was added to the mixture. This process was carried out in a high shear reactor with vigorous stirring for 20 minutes. The addition is then stopped. This means that dry Na ₂CO₃ with a total mass of 1660g was added to the mixture, which corresponds to a 1:1 stoichiometric ratio between calcium ions (Ca ²⁺) and carbonate ions (CO ₃ ^2-).

TABLE 1 physical data of Precipitated Calcium Carbonate (PCC) obtained in examples 1-4

The inventors have shown that the morphology of the precipitated calcium carbonate product obtained can be controlled by the process of the invention. Scalenohedral PCC products were obtained in inventive examples 2-4, while vaterite was obtained in comparative example 1, as can be seen from table 1 and fig. 1.

TABLE 2 physical data of Precipitated Calcium Carbonate (PCC) obtained in examples 5-9

*0.6% Calcite (Ca (OH) ₂) as trace impurity

SEM images of the products of examples 5-9 of the present invention showed scalenohedral crystal morphology, as can be seen from fig. 5-9.

Reference example 1

As a reference example, precipitated calcium carbonate was prepared according to the working scheme of example 10 of US 2006/019.6836 A1, except that Reverse Osmosis (RO) concentrate was simulated from a comparable but synthetically prepared solution having the following ion concentrations:

18 Mg/L Mg (from 150.3 Mg/L MgCl ₂ x 6H₂ O)

90 Mg/L Ca (from 330.1 mg/L CaCl ₂ x 2H₂ O)

11600 Mg/L bicarbonate (NaHCO ₃ from 16.0 g/L)

0.1 Mg/L sulfate (from 0.26 Mg/L Mg (SO ₄) x 7H₂ O)

11300 Mg/L chloride ion (from 18.3 g/L NaCl)

Total dissolved solids content 34g/L. The reaction was carried out in a laboratory reactor. When CaCl ₂ solution (18% by weight) is added, the pH of the second reaction is reduced to a final value of 7.2, contrary to the description of example 10 in this us patent, which indicates that the pH in the second reaction results in a pH value of 10.2-10.5.

The final product obtained in reference example 1 had a fine, block, prismatic calcite shape with d ₅₀ (Sedigraph) of 2.94 μm and SSA of 5.3m ²/g. According to geochemical analysis (XRD), the purified product contained 100% calcite. SEM images of the final product obtained in reference example 1 are shown in fig. 10.

Reference example 2

As another reference example, precipitated calcium carbonate was prepared according to the working scheme of example 11 of US 2006/019.6836 A1, except that Reverse Osmosis (RO) concentrate was simulated from a comparable but synthetically prepared solution having the following ion concentrations:

3700 mg/L sodium (from 1.2 g/L NaCl)

74 Mg/L potassium (from 141.2 mg/L KCl)

120 Mg/L magnesium (from 698.7 mg/L MgCl ₂ x 6H₂ O)

49 Mg/L calcium (from 179.7 mg/L CaCl ₂ x 2H₂ O)

8540 Mg/L bicarbonate (from 11.8 g/L NaHCO ₃)

144 Mg/L sulfate (from 369.5 Mg/L Mg (SO ₄) x 7H₂ O)

550 Mg/L chloride ion

The total dissolved solids content was 13.2 g/L.

The reaction was carried out in a laboratory reactor. The final product of the second reactor obtained in reference example 2 had a coarse, block, prismatic calcite shape with d ₅₀ (Sedigraph) of 6.8 μm and SSA of 1.6m ²/g. According to geochemical analysis (XRD), the purified product contained 100% calcite. SEM images of the final product obtained in reference example 2 are shown in fig. 11.

Claims

1. A method for producing a triangular-faceted PCC product, the method comprising the following steps:

a) Provides at least one calcium compound selected from calcium oxide powder, calcium hydroxide powder, and calcium hydroxide suspension;

b) Provide a calcium chloride solution containing 0.5-270 g/L of calcium;

c) Mix the at least one calcium compound from step a) and the calcium chloride solution from step b) in any order.

In the obtained mixture, the molar ratio of the at least one calcium compound in step a) to the calcium chloride in step b) is 7:93 to 80:20.

d) Add a sodium carbonate source, selected from sodium carbonate or a mixture consisting of at least 70% by weight sodium carbonate and at a pH of 9.5-13.5, to the mixture obtained in step c) at a temperature of 30-70°C and a pH of 9.5-13.5.

The total calcium-containing materials in steps a) and b) and the sodium carbonate source in step d) have a calcium ion to carbonate ion molar ratio (Ca ²⁺ : CO ₃ ^2- ) of 1.00:1.00 to 1.00:1.30.

2. The method according to claim 1, wherein the at least one calcium compound in step a) is calcium hydroxide powder or calcium hydroxide suspension, preferably calcium hydroxide suspension, and preferably, the calcium hydroxide suspension has a solid content of 5-50% by weight, preferably 7-47% by weight and most preferably 9-45% by weight based on the total weight of the calcium hydroxide suspension.

3. The method according to any one of the preceding claims, wherein the at least one calcium compound in step a) is in the form of calcium hydroxide particles having a volumetric particle size _d50 (vol) of 0.05-25 μm, preferably 0.2-10 μm, more preferably 0.4-5 μm and most preferably 1.0-3.5 μm, and/or a volumetric particle size _d90 (vol) of 0.15-75 μm, preferably 1-30 μm, more preferably 1.5-15 μm and most preferably 2-10 μm.

4. The method according to any one of the preceding claims, wherein the calcium chloride solution in step b) comprises 1.0-200 g/L, preferably 2.0-150 g/L, more preferably 3.0-100 g/L, and most preferably 5.0-50 g/L of calcium.

5. The method according to any one of the preceding claims, wherein in step c), the molar ratio of the at least one calcium compound of step a) to the calcium chloride of step b) in the obtained mixture is 10:90 to 70:30, preferably 15:85 to 50:50, more preferably 20:80 to 40:60 and most preferably about 25:75.

6. The method according to any one of the preceding claims, wherein the temperature in step d) is 40-60°C, more preferably 45-50°C and/or wherein the pH value is 10.0 to 13.0 and more preferably 10.5 to 12.0.

7. The method according to any one of the preceding claims, wherein the sodium carbonate source is added to the mixture obtained in step c) in at least two portions.

The first portion comprises 0.01-5% by weight of the total sodium carbonate source and is added in the form of a solution containing 5-20 g/L of the sodium carbonate source. Preferably, the first portion of the sodium carbonate source in step d) comprises 0.1-4.0% by weight of the total sodium carbonate source, more preferably 1.0-3.0% by weight, and most preferably 1.5-2.5% by weight, and/or

It is added in the form of a solution containing 7-17 g/L, preferably 8-15 g/L of the sodium carbonate source.

8. The method of claim 7, wherein the sodium carbonate source remaining after the first portion is added as a second portion in a single step, and/or wherein the sodium carbonate source remaining after the first portion is added as a solid, and/or

The sodium carbonate source is sodium carbonate.

9. The method according to any one of the preceding claims, wherein the total amount of calcium-containing materials in steps a) and b) and the sodium carbonate source in step d) have a molar ratio of calcium ions to carbonate ions ( ^Ca²⁺ : _CO³²⁻ ) of 1.00:1.00 to ^1.00 :1.20, more preferably 1.00:1.00 to 1.00:1.10 and most preferably about 1.00:1.05.

10. The method according to any one of the preceding claims, wherein the method further comprises step e): adding an additive, preferably a dispersant and/or a nucleating agent, such as sucrose or citrate, and most preferably sucrose, to the mixture obtained in step c).

11. The method according to any one of the preceding claims, wherein the method further comprises step f): separating the triangular PCC product from the aqueous suspension obtained in step d), and preferably, step f) is performed by solvent evaporation and/or pressure filtration, and/or

The method further includes step g): after step d) or, if present, after step f), drying the triangular PCC product at a temperature of 60-120°C, preferably 80-110°C and most preferably 95-105°C, preferably until the moisture content of the triangular PCC product is less than 1% by weight, based on the total weight of the dried triangular PCC product.

12. The method according to any one of the preceding claims, wherein the calcium chloride solution in step b) is a waste material, preferably obtained from a recycling process, and more preferably from an aqueous inorganic luminescent material recycling process, and/or wherein the calcium chloride solution contains additional salts, preferably selected from magnesium salts, sodium salts and potassium salts, and most preferably selected from magnesium chloride, sodium chloride and potassium chloride.

13. The method according to any one of the preceding claims, wherein the calcium chloride solution in step b) comprises a magnesium salt, and preferably, the solution comprises 5-200 mg/L, more preferably 5-100 mg/L and most preferably 5-50 mg/L of magnesium.

14. The method according to any one of the preceding claims, wherein the obtained triangular-faceted PCC product

i) Having a specific surface area of 0.1-25.0 ^m² /g, preferably 0.5-20.0 ^m² /g and most preferably 1.0-15.0 ^m² /g, measured using nitrogen and the BET method according to ISO 9277:2010, and/or

ii) is in the form of particles having a volume-based median particle size _d50 (vol) of 0.05-10 μm, preferably 0.2-8 μm, more preferably 0.4-5 μm, and most preferably 1.0-3.5 μm, and/or

iii) is the form of a particle having a volume-based apical particle size d ₉₈ (vol) of 0.15-20 μm, preferably 1-15 μm, more preferably 1.5-10 μm, and most preferably 2-8 μm, and/or

iv) having an ISO whiteness (R457) of at least 90%, preferably at least 92%, more preferably at least 95%, and most preferably at least 97%; and/or

v) A yellowness index (YI) lower than 2, preferably lower than 1.8, more preferably lower than 1.6, and most preferably 0.5-1.5, and/or

vi) comprising triangular PCC products with a total dry weight of at least 80%, preferably 90%, and most preferably 95%, of triangular PCC products, and aragonite products with a total dry weight of 20%, preferably 10%, and most preferably 5%, of triangular PCC products.

15. A triangular-faceted PCC product obtainable according to any one of claims 1-14.

16. Use of the triangular-faceted PCC product according to claim 15 in polymer applications, paper coating applications, papermaking, paints, coatings, sealants, adhesives, feed, pharmaceuticals, concrete, cement, cosmetics, water treatment, engineered wood applications, gypsum board applications, packaging applications, catalysis, gas treatment applications and/or agricultural applications.