Method for producing precipitated calcium carbonate (pcc), pcc product and use of pcc

Abstract

Methods of making precipitated calcium carbonate are provided. The method includes providing a suspension having calcium hydroxide, and adding processed white mud to the suspension followed by carbonation to precipitate calcium carbonate.

Description

Technical Field

[0001] The present invention relates to a method for producing precipitated calcium carbonate (PCC). In addition, the present invention relates to an aqueous suspension of PCC, the produced PCC and products made from the produced PCC. More specifically, the present invention relates to a method for producing PCC using processed lime mud. Background Art

[0002] Precipitated calcium carbonate (PCC), which has the chemical formula CaCO3, exists in three main crystalline forms: calcite, aragonite and vaterite. PCC can have many different polymorphs. Crystal habits can include scalenohedral, rhombohedral, hexagonal prisms, cubic and prismatic. PCC is prepared by introducing CO2 into an aqueous suspension of calcium hydroxide (Ca(OH)2), which is commonly referred to as "milk of lime":

[0003] Ca(OH)2+CO2→CaCO3+H2O

[0004] PCC is widely used in the papermaking industry. PCC is inexpensive and is used as a bulking material. PCC increases the brightness and opacity of paper. Therefore, PCC is considered to be an excellent filler material for paper and paperboard. However, PCC can also affect the "sizing" of paper, which is a term commonly used in the art to quantify or describe the hydrophobic treatment of paper fibers. Poor paper sizing will result in poor printability (such as ink stains) and reduced print quality. Fillers such as PCC and ground calcium carbonate (GCC) used for paper can compete with paper fibers for sizing chemicals, resulting in reduced sizing performance. Changes in PCC production can affect the specific surface area (SSA) of PCC particles, aggregates or agglomerates. For example, large changes in SSA can be attributed to changes in the quality of the lime used. A large amount of impurities such as silicon (Si) and magnesium (Mg) in lime can increase the SSA of PCC. An increase in the SSA of PCC can result in a reduction in paper sizing performance.

[0005] The morphology of PCC can also affect the sizing of paper. PCC fillers with scalenohedral morphology aggregate into clusters, which in turn provide a more porous structure. This structure can consume sizing chemicals such as alkyl ketene dimer (AKD) and alkenyl succinic anhydride (ASA). AKD is a reactive synthetic sizing agent that is used in alkaline or neutral papermaking conditions to provide a certain level of hydrophobicity to the paper. ASA is an alkaline or neutral type of sizing agent and is used as an internal sizing chemical in paper mills. The consumption of sizing chemicals by the porous structure of PCC hinders the ability of the chemicals to promote paper sizing to an acceptable level, thereby reducing the effectiveness of the sizing chemicals.

[0006] Although PCC is the primary filler and bulking additive for paper, PCC can be combined with white mud to be used as a paper filler. White mud is physically blended with PCC, and the mixture is then used in papermaking. White mud is a byproduct produced in pulp mills as part of the process of converting wood chips into paper pulp. Therefore, this byproduct can be recycled back into paper to reduce waste. In addition, white mud is cheaper than PCC, and supplementing PCC with white mud further reduces papermaking costs.

[0007] However, the use of certain types of lime mud can result in poor paper sizing. Some types of lime mud include relatively high amounts of silicon (Si), including non-wood-based lime muds (e.g., agricultural, bamboo, and straw pulp lime muds), and lime muds produced by pulping processes (e.g., alkaline peroxide mechanical pulping (APMP) and bleached chemithermomechanical pulping (BCTMP)), where silicates / Si are used to stabilize bleaching chemicals. These amounts can be as high as 10+% SiO2, but even lower amounts such as 2% SiO2 can adversely affect the quality of the paper. The high Si amount is converted into fine amorphous silica particles, which results in a high SSA of the lime mud. When the SSA of the lime mud is high, paper sizing can be reduced to unacceptable levels. Fillers with high SSA levels consume more sizing chemicals such as AKD and ASA.

[0008] Embodiments of the present invention are directed to solving, inter alia, the above-mentioned problems by producing PCC and lime mud filler materials having suitable SSA and morphology for use with paper to improve sizing and printability. Summary of the invention

[0009] According to one aspect of the present invention, there is provided a method for producing a suspension of precipitated calcium carbonate (PCC). The method may include: (a) adding a suspension comprising processed white mud to a suspension comprising calcium hydroxide; and (b) carbonating the suspension comprising processed white mud and calcium hydroxide to form a resulting suspension comprising PCC. The processed white mud may have a weight median diameter d of at least 0.3 μm. 50 The processed white mud may have a weight median diameter d of 0.3 μm to 10 μm. 50. According to one embodiment, the total amount of processed white mud used in the method may be an amount of 0.3 wt % to 80 wt % based on the total weight of the dry PCC to be prepared. The white mud used to make the processed white mud may be a by-product of alkali recovery in pulping and papermaking. In one embodiment, before the carbonation of the suspension in step (b) begins, the entire amount of the suspension comprising processed white mud is added to the suspension comprising calcium hydroxide. In one embodiment, the addition of the suspension comprising processed white mud in step (a) begins before the carbonation step (b) begins, continues during the carbonation step (b), and ends when or before the pH of the reaction contents of the carbonation step (b) reaches a value of 9 or 10. In one embodiment, the addition of the suspension comprising processed white mud in step (a) continues during a portion of the carbonation step (b), and ends before the carbonation step (b) ends. Processed white mud can be made by a method comprising the following steps: (a) providing an aqueous suspension of white mud; (b) dehydrating the white mud suspension to produce dehydrated white mud solids; (c) washing the dehydrated white mud solids and producing a washed white mud suspension; (d) sieving the washed white mud suspension to remove white mud solids and / or grit particles of a selected size from the washed white mud suspension; (e) grinding the sieved white mud suspension; and (f) neutralizing the ground white mud suspension with a material containing a non-metallic oxide to produce processed white mud. The method may also include hydrating lime to form a suspension comprising calcium hydroxide. The carbonation step (b) may cause PCC crystals to grow on the processed white mud crystal clusters.

[0010] According to another aspect of the present invention, a method for manufacturing a filler comprising precipitated calcium carbonate (PCC) is provided. The method comprises: (a) combining ingredients comprising calcium oxide and water to prepare a slurry comprising calcium hydroxide; (b) supplying processed white mud to the slurry comprising calcium hydroxide to form a resultant comprising processed white mud and calcium hydroxide; and (c) subjecting the resultant comprising processed white mud and calcium hydroxide to a carbonation process to form a suspension comprising PCC. The precipitated calcium carbonate may encapsulate processed white mud particles or crystal clusters. In one embodiment, the supply of processed white mud ends before the carbonation process begins. In one embodiment, performing the carbonation process includes adding a material that generates carbon dioxide to the resultant comprising processed white mud and calcium hydroxide, and the method further includes ending the supply of processed white mud to the slurry before the material that generates carbon dioxide is added to the resultant. In one embodiment, performing the carbonation process includes adding a material that generates carbon dioxide to the resultant comprising processed white mud and calcium hydroxide, and wherein the supply of processed white mud continues during a portion of the carbonation process. In one embodiment, the supply of processed lime mud continues during the carbonation process and ends when or before the pH reaches a value of 9 or alternatively 10. The method may also include: (d) separating the precipitated calcium carbonate and the processed lime mud from the suspension; and (e) drying the separated solids to form a dried precipitated calcium carbonate and processed lime mud composite. The total amount of processed lime mud used in the method may be an amount of 0.3 wt% to 80 wt% based on the total weight of the dry PCC to be prepared. The processed white mud can be manufactured by a method comprising the following steps: (a) providing an aqueous suspension of white mud, which is a by-product of alkali recovery in pulping and papermaking; (b) dewatering the white mud suspension to produce dehydrated white mud solids; (c) washing the dehydrated white mud solids and producing a washed white mud suspension; (d) sieving the washed white mud suspension to remove white mud solids and / or grit particles of a selected size from the washed white mud suspension; (e) grinding the sieved white mud suspension; and (f) neutralizing the ground white mud suspension with a material containing non-metallic oxides to produce processed white mud. The processed white mud may have a weight median diameter d of 0.3 μm to 10 μm. 50 .

[0011] According to another aspect of the present invention, a method for producing precipitated calcium carbonate is provided. The method may include: (a) hydrating calcium oxide to form slaked lime; (b) adding an aqueous suspension of processed lime mud to slaked lime; and (c) adding a material generating carbon dioxide to form an aqueous suspension of precipitated calcium carbonate coated on the processed lime mud, wherein (i) the addition of the aqueous suspension of processed lime mud begins and ends before the addition of the material generating carbon dioxide begins, or (ii) the addition of the aqueous suspension of processed lime mud begins before the addition of the material generating carbon dioxide begins, continues during the addition of the material generating carbon dioxide, and ends when or before the pH of the reaction contents of step (c) reaches a value of 9 or 10, or (iii) the addition of the aqueous suspension of processed lime mud and the addition of the material generating carbon dioxide begin simultaneously, and the addition of the aqueous suspension of processed lime mud ends when or before the pH of the reaction contents of step (c) reaches a value of 9 or 10. The method may also include: (d) separating the precipitated calcium carbonate and the processed white mud from the aqueous suspension; and (e) drying the separated solid to form a dried precipitated calcium carbonate at least partially coated on the processed white mud. The total amount of processed white mud used may be greater than 0.3 wt % and less than 80 wt % based on the total amount of dried precipitated calcium carbonate. The processed white mud may have a weight median diameter d of 0.3 μm to 10 μm. 50 .

[0012] According to another aspect of the present invention, there is provided a paper product comprising precipitated calcium carbonate produced by the method of the present invention and processed lime mud.

[0013] According to another aspect of the present invention, there is provided a filler material comprising precipitated calcium carbonate grown on processed lime mud particles produced by the method of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A method for producing precipitated calcium carbonate according to one embodiment of the present invention is shown.

[0015] Figure 2 A method of producing a processed lime mud suspension according to one embodiment of the present invention is shown.

[0016] Figure 3 It is a graph of Cobb value versus specific surface area (SSA) for Example 1.

[0017] Figure 4 A comparative method of producing precipitated calcium carbonate according to Example 2 is shown.

[0018] Figure 5 is a plot of Cobb value versus ash percentage for Example 2.

[0019] Figure 6This is the form of the sample of Example 2.

[0020] Figure 7 This is the form of the sample of Example 2.

[0021] Figure 8 This is the form of the sample of Example 2.

[0022] Fig. 9 This is the form of the sample of Example 2. DETAILED DESCRIPTION

[0023] As used herein, precipitated calcium carbonate (PCC) adopts its common chemical definition with chemical formula CaCO3.PCC has three main crystalline forms: calcite, aragonite and vaterite.It can also include a plurality of different polymorphs or crystal habits of each in these crystalline forms.For embodiments of the present invention, the crystal habit can be preferably scalenohedron (S-PCC).

[0024] As used herein, calcium hydroxide adopts its common chemical definition with chemical formula Ca(OH)2. Calcium hydroxide is traditionally called "slaked lime" or "lime milk", and slaked lime, slaked lime, lime milk and slurry with calcium hydroxide are terms used interchangeably herein. Slaked lime is produced when calcium oxide or quicklime is mixed with water or slaked or hydrated with water. Calcium hydroxide has many other names, including hydrated lime, caustic lime, building lime and pickling lime. Slaked lime can be a calcium hydroxide slurry such as an aqueous calcium hydroxide suspension, and can, for example, have a solid content of less than 40% by weight.

[0025] As used herein, calcium oxide adopts its common chemical definition having the chemical formula CaO. Calcium oxide is commonly known as lime or quicklime, and is an alkaline substance.

[0026] As used herein, a calcium oxide containing compound or material is a material having at least 40 wt% calcium oxide based on the total weight of the material. Preferably the content is at least 70 wt%, and more preferably at least 90%.

[0027] As used herein, a slurry is a mixture of solids suspended in a liquid, usually water. The suspension may include insoluble solids, water, and optional additives.

[0028] As used herein, white mud adopts its common chemical definition and can be a by-product produced, for example, in a pulp mill as part of a process of converting wood chips into paper pulp. White mud can be a by-product of alkali recovery in pulping and papermaking. The pulp mill processes or "cooks" wood chips with an alkaline pulping liquor containing sodium hydroxide or a blend of sodium hydroxide and sodium sulfide to extract wood fibers for papermaking. During this process, the sodium hydroxide is converted into sodium carbonate. The pulp mill then adds calcium oxide or quicklime to convert the sodium carbonate back into sodium hydroxide to reuse it. Calcium carbonate is formed in this process. Calcium carbonate is the main component of white mud. Although white mud is mainly calcium carbonate, it can also contain, for example, silicon dioxide, magnesium carbonate and trace amounts of nitrogen, calcium, potassium oxide, phosphorus pentoxide, magnesium, sulfur, boron, copper and / or zinc. White mud can be synthesized from lime and water and Na2CO3. The main chemical reactions that occur during the causticizing process of papermaking white mud are as follows:

[0029] CaO+H2O→Ca(OH)2

[0030] Ca(OH)2+Na2CO3→2NaOH+CaCO3↓

[0031] As used herein, processed lime mud is lime mud that has undergone a treatment step. The treatment step may include, but is not limited to, for example, dewatering, washing, screening, grinding and / or neutralization.

[0032] As used herein, the compound or material that generates carbon dioxide may include, but is not limited to, for example, gaseous carbon dioxide, liquid carbon dioxide, solid carbon dioxide, gas or liquid containing carbon dioxide (e.g., Na2CO3, K2CO3, etc.), pure gaseous carbon dioxide, and flue gas containing carbon dioxide. The compound that generates carbon dioxide may be a gaseous mixture of carbon dioxide and air or carbon dioxide and nitrogen.

[0033] As used herein, carbonation (or carbonation) refers to the process of converting calcium hydroxide into PCC. This conversion can be carried out by adding or supplying a certain amount or volume (e.g., kg CO2 / min / kg dry Ca (OH)2) of a compound producing carbon dioxide in the slaked lime of a reaction vessel. The completion of carbonation can be extended to after the addition of the compound producing carbon dioxide is completed, and the addition of the compound producing carbon dioxide can be continuous or intermittent.

[0034] As used herein, reaction contents are defined as the contents contained in the reaction vessel during a carbonation process (such as a suspension being carbonated). Contents may include, but are not limited to, aqueous phases, compounds that generate carbon dioxide, calcium hydroxide slurries, processed white mud, precipitated calcium carbonate that has been formed, and / or additives that may have been added during the process. For example, when referring to the pH of a suspension or a carbonation process, this is intended to represent the pH of the reaction contents when the measurement is performed.

[0035] As used herein, an aqueous suspension refers to a system in which the liquid phase comprises, consists essentially of, or consists of water. The term may include water in combination with a small amount of a water-miscible organic solvent such as methanol, ethanol, acetone, acetonitrile, tetrahydrofuran, and combinations thereof.

[0036] As used herein, specific surface area or SSA is determined by the BET method (Brunauer, Emmet, Teler, ISO 9277) which is well known in the art.

[0037] As used herein, particle size refers to the weight-based distribution of particle sizes dx. The value of dx represents a diameter relative to which x weight % of the particles have a diameter less than dx. The particle size values ​​disclosed herein are measured by sedimentation methods such as Sedigraph particle size analysis, which is well known in the art.

[0038] As used herein, the solids content of a liquid composition refers to the amount of solid material remaining after all solvent and / or water has been removed and / or evaporated, measured in weight percent.

[0039] As used herein, coating can mean that a substrate is completely or partially covered with another material. For example, when particle A is referred to as being coated with compound B, this means that compound B completely or at least partially covers the surface of particle A, and compound B can be physically connected and / or chemically bonded to particle A.

[0040] As used herein, the singular forms "a", "an", and "the" are intended to include the plural forms and the plural is intended to include the singular, unless the context clearly indicates otherwise (such as use of the terms "one" or "plurality"). For example, a reaction content may include more than one content.

[0041] As used herein, the term "and / or" includes any combination of one or more of the associated listed items.

[0042] Figure 1An embodiment of a method for making precipitated calcium carbonate (PCC) is shown. A material containing calcium oxide or quicklime is added to water or hydrated to form slaked lime or a slurry with calcium hydroxide. The slaked lime can be sieved to remove particles of undesirable size. Before the carbonation process by introducing a material producing carbon dioxide begins, an aqueous suspension comprising processed white mud (or consisting essentially of processed white mud, or consisting of processed white mud) is added to the slaked lime or slurry. The processed white mud can be added in dry form.

[0043] In one embodiment, the addition of the suspension (or in dry form) of processed white mud can be started and ended before the carbonation process begins or before the addition of the material generating carbon dioxide. That is, all of the processed white mud is added to the slaked lime before the carbonation process begins or before the addition of the material generating carbon dioxide, and processed white mud is not added at any time point during the carbonation process. The addition or supply of processed white mud and / or the material generating carbon dioxide can be continuous or intermittent.

[0044] In one embodiment, the addition of processed white mud (e.g., suspension or dry form) begins before the carbonation process begins or the material that generates carbon dioxide is added, continues during the addition of a part of the carbonation process or the material that generates carbon dioxide, and ends before the carbonation process terminates or the addition of the material that generates carbon dioxide terminates. The addition or supply of processed white mud and / or the material that generates carbon dioxide can be continuous or intermittent. In one embodiment, the addition of processed white mud is stopped completely when or before the pH of the reaction content reaches a pH of 10 or 9 that is substituted, and processed white mud is no longer added after the pH reaches 10 or 9 that is substituted. From the beginning to the end of the carbonation process, the pH value of the reaction content decreases. For example, the pH value can be 12-13 when the carbonation process begins, and can be 7-8 when the carbonation process ends.

[0045] In one embodiment, the addition of processed white mud (such as suspension or dry form) and the beginning of carbonation process or the beginning of the addition of carbon dioxide-containing material start simultaneously, and the addition of processed white mud ends before the carbonation process ends or the addition of carbon dioxide-containing material stops. The addition or supply of processed white mud and / or the material producing carbon dioxide can be continuous or intermittent. In one embodiment, the addition of processed white mud is stopped completely when or before the pH of the reaction content reaches a pH of 10 or 9 that replaces, and processed white mud is no longer added after the pH reaches 10 or 9 that replaces. Similarly, as mentioned above, the pH value of the reaction content decreases from the beginning of carbonation process to the end. For example, the pH value can be 12-13 when the carbonation process begins, and can be 7-8 when the carbonation process ends.

[0046] The carbonation process can produce an aqueous suspension comprising PCC and processed white mud. The method can produce a compound or complex of PCC and processed white mud. PCC crystals can grow on processed white mud particles, cores or crystal clusters. Processed white mud can be coated with PCC. The method of an embodiment of the present invention may also include separating PCC from the resulting aqueous suspension, and drying PCC and processed white mud. Separation, filtering and drying steps can be used to form dry PCC and processed white mud (e.g., processed white mud coated or encapsulated with PCC). The total amount of processed white mud used in the method or added to slaked lime can be greater than 0.3% by weight to less than 80% by weight, preferably 1.0% by weight to 40% by weight, based on the total weight of the dry PCC to be produced, or the solid PCC content to be produced, or the material containing dry calcium carbonate to be produced (i.e., a compound or complex comprising processed white mud (essentially composed of processed white mud or composed of processed white mud) and PCC).

[0047] Figure 2 It is an exemplary embodiment for producing processed white mud. In step 100, an aqueous suspension of white mud is provided. In step 110, the suspension is dehydrated to produce dehydrated white mud solids. In step 120, the dehydrated white mud solids can be washed. The white mud solids can also be diluted into the washed white mud suspension. In step 130, the washed white mud suspension is subjected to a screening process to remove white mud solids and / or grit particles of selected size from the washed white mud suspension. In step 140, the screened white mud suspension is ground. In step 150, the ground white mud suspension is neutralized with a material containing non-metallic oxides to produce processed white mud. The material containing non-metallic oxides can include CO2, SO2, SO3 and mixtures thereof. Non-metallic oxides can be introduced into the white mud suspension in solid, liquid or gaseous form. An aqueous suspension of processed lime mud as an additive (e.g., a precipitation additive for PCC) is produced, wherein the processed lime mud has a weight median diameter d of at least 0.3 μm, preferably 0.3 μm to 10 μm. 50 .

[0048] It will be further appreciated that various additives may be added before and after the carbonation process. For example, an additive may be added to the milk of lime. The additive may be, for example, a slaking additive or a precipitation additive. The example of an additive comprises sugar, citric acid, potassium, sodium and other additives well known in the art. In addition, the method of the present invention may be carried out in batch, semi-batch or continuous mode. The continuous mode may be carried out in a continuous tubular reactor or in several separate carbonators (the pH of the suspension is gradually reduced from the first carbonator to the last carbonator).

[0049] Fillers and additives made by the method of the present invention can be used in paper (which is intended to include paperboard and all paper products). Fillers and additives made by the method of the present invention can also be used in consumer products, including but not limited to coatings, paints, rubbers, plastics, polymers, building materials, inks, foods, cosmetics, agricultural products, drugs and pharmaceuticals.

[0050] According to an embodiment of the present invention, adding processed white mud to slaked lime can produce a filler material comprising a composite or complex of processed white mud and PCC (or consisting of it if no other fillers are added). The processed white mud particles, cores or crystal clusters can be coated with PCC. The PCC preferably has a scalenohedral crystal structure (S-PCC). The method of the present invention allows PCC to be synthesized and grown on processed white mud particles during the carbonation process. The precipitated calcium carbonate crystals grow together with processed white mud particles, cores or clusters and encapsulate processed white mud particles, cores or clusters. The precipitated calcium carbonate can coat processed white mud particles. The SSA of the produced filler material (i.e., processed white mud coated with PCC) can be reduced by up to 45% compared to the SSA of a blend of processed white mud and PCC when white mud of the same amount, type and size and comparable PCC are blended after the carbonation process.

[0051] For example, the SSA of 25% processed white mud coated with 75% PCC is less than the SSA of 25% processed white mud blended with 75% PCC after the carbonation process. Compared with physically blending the same two components after manufacturing each component after the carbonation process, adding processed white mud to slaked lime according to the method of the present invention provides an unexpected effect of reducing SSA. The method of the present invention also produces PCC (e.g., S-PCC) with less porosity and a more solid structure. The lower porosity prevents or minimizes the consumption of sizing chemicals (e.g., AKD, ASA, and rosin) added during papermaking. The lower filler SSA improves paper quality by enhancing paper sizing. Enhanced paper sizing reduces the extent to which ink can be stained on the surface of the paper. The method of the present invention allows the use of lower cost and quality white mud to supplement PCC fillers, because it is believed that the higher amount of impurities in low-quality white mud will not significantly affect the reduction of SSA and PCC porosity achieved by the method of the present invention.

[0052] Example

[0053] Example 1

[0054] raw material:

[0055] Lime A was collected from the lime silo of Specialty Minerals Inc. XRF analysis showed that Lime A had high Si (4.8% in the form of SiO2).

[0056] Processed Lime Mud (PLM) is made from non-wood based lime mud produced from caustic / APMP (Alkaline Peroxide Mechanical Pulp) pulping process, which contains a large amount of silicon, where silicate / silicon is used to stabilize the bleaching chemical properties, which leads to high SSA. The properties of PLM are shown in Table 1 as "PLM".

[0057] Laboratory Process:

[0058] 1. Prepare an aqueous suspension of a precipitated calcium carbonate (PCC) control.

[0059] The PCC control was synthesized in the laboratory from lime A based on a standard laboratory synthesis method:

[0060] Slaked lime was prepared by using lime A and water, wherein the ratio of lime to water was 1:7. Carbonation was carried out in a 4 L laboratory reactor equipped with a stirrer stirring at 1250 rpm. The gas was 15% CO2 and 85% air. Carbonation was started at 50°C by injecting CO2 until the pH reached 7.5. The CO2 was suspended for 5 min and then the slurry was recarbonated to pH 7.5. The properties of this PCC control are shown in Table 1 as "PCC1".

[0061] 2. Prepare a mixed PCC control with PLM filler (comparative method).

[0062] The mixed PCC control with PLM filler is as follows Figure 4 The mixing ratio of PCC1 and PLM filler was 80:20 on a dry weight basis. The properties of the mixed PCC1-PLM are shown in Table 1 as "Mixed 20PLM80PCC1".

[0063] 3. Pass Figure 1 The aqueous suspension of PCC filler was prepared by the method.

[0064] The PCC filler of an embodiment of the present invention was synthesized in the laboratory from lime A and PLM filler. The slaked lime was prepared using lime A and water, wherein the ratio of lime to water was 1:7. Carbonation was carried out in a 4L laboratory reactor equipped with a stirrer stirring at 1250rpm. The gas was 15% CO2 and 85% air. Carbonation was started at 50°C by injecting CO2 until the pH reached 7.5. The CO2 was suspended for 5min and then the slurry was recarbonated to pH 7.5. Prior to carbonation, 20% by weight of PLM filler based on the final total weight of calcium carbonate was added to the slaked lime as an additive (i.e., before carbonation began). The properties of the synthesized new PCC are shown as "NPCC" in Table 1.

[0065] Table 1: Characteristics of laboratory test fillers

[0066]

[0067] From Table 1, PLM has a high SSA (16.1m 2 PCC1 is made using low-quality lime with more impurities, which results in a high SSA (14.9 m 2 Finally, the SSA of the mixed 20PLM80PCC1 has a high SSA (16.6 m 2 / g). Under the same ratio of PLM, the SSA of NPCC decreased (10.2m 2 / g), even lower than the SSA of PCC1. This method can reduce the negative impact of high SSA from PLM and also improve the quality of PCC.

[0068] Handsheet sizing tests were conducted using PCC1, mixed 20PLM80PCC1 and NPCC. Figure 3 NPCC has the lowest Cobb value, which can enhance paper sizing.

[0069] Example 2

[0070] Slaked lime was prepared using lime B and water, wherein the ratio of lime to water was 1 : 7. The slaked lime was distributed to 2 carbonators to conduct plant trials using the same quality of slaked lime.

[0071] Figure 4 Route - Comparative Route: In a carbonator, slaked lime was carbonated to produce a PCC control which was then blended with a PLM filler at a ratio of 36% based on the final total weight of calcium carbonate. The properties of the prepared PCC control / PLM filler mixture are shown in Table 2 as PCC1 / PLM / Mixed 36PLM64PCC1. The morphology of PCC1 is as follows Figure 6 As shown in Figure 2, the form of PLM is as follows: Figure 7 As shown, and the morphology of the mixed 36PLM64PCC1 is as follows Figure 8 shown.

[0072] Figure 1 Route: Before carbonation, slaked lime was mixed with PLM filler. The ratio of PLM filler was 36% based on the final total weight of calcium carbonate. Carbonation was initiated on the mixed slaked lime and PLM filler to produce new PCC filler. The properties of the new PCC filler prepared in this plant are shown as "NPCC" in Table 2. The morphology of NPCC is as follows Fig. 9 shown.

[0073] Table 2: Characteristics

[0074]

[0075] From Table 2, compared with the conventional route (mixed 36PLM64PCC1), the SSA of the new route (NPCC) is reduced by 22%, from 10.6m 2 / g dropped to 8.3m 2 / g. The SSA of the new route (NPCC) has been reduced to the same level as PCC1.

[0076] Handsheet sizing tests were conducted using PCC1 and NPCC. The results are shown in Figure 5 The Cobb value of NPCC is reduced, which results in improved sizing. From the morphological comparison, NPCC has more solid core structure, while PCC1 has a porous structure.

[0077] Although several specific forms, variations and embodiments of the present invention have been shown and described, it will be apparent that various changes may be made without departing from the scope of the present invention. It is also contemplated that different combinations or sub-combinations of the specific features and aspects of the disclosed embodiments may be combined or substituted with one another to form different modes of the present invention.

Claims

1. A method for producing a precipitated calcium carbonate (PCC) suspension, comprising: (a) adding a suspension comprising processed lime mud to a suspension comprising calcium hydroxide; and (b) carbonating a suspension comprising said processed lime mud and said calcium hydroxide to form a resulting suspension comprising PCC.

2. The method according to claim 1, wherein the processed lime mud has a weight median diameter d of at least 0.3 μm. 50 .

3. The method according to claim 1, wherein the processed lime mud has a weight median diameter d of 0.3 μm to 10 μm. 50 .

4. The process as claimed in claim 1, wherein the total amount of the processed lime mud used in the process is in an amount of 0.3 wt% to 80 wt% based on the total weight of dry PCC to be prepared.

5. The method according to claim 1, wherein the lime mud used to make the processed lime mud is a by-product of alkali recovery in pulping and papermaking.

6. The method according to claim 1, wherein the entire amount of the suspension comprising processed lime mud is added to the suspension comprising calcium hydroxide before the carbonation of the suspension in step (b) is started.

7. The method according to claim 1, wherein the addition of the suspension comprising processed lime mud in step (a) begins before the start of the carbonation step (b), continues during the carbonation step (b), and ends before or when the pH of the reaction contents of the carbonation step (b) reaches a value of 9 or 10.

8. The method of claim 1, wherein the adding of the suspension comprising processed lime mud in step (a) continues during a portion of the carbonation step (b) and ends before the carbonation step (b) ends.

9. The method according to claim 1, wherein the processed lime mud is produced by a method comprising: (a) providing an aqueous suspension of lime mud; (b) dewatering the lime mud suspension to produce dewatered lime mud solids; (c) washing the dewatered lime mud solids and producing a washed lime mud suspension; (d) screening the washed lime mud suspension to remove lime mud solids and / or grit particles of a selected size from the washed lime mud suspension; (e) grinding the sieved lime mud suspension; and (f) neutralizing the ground lime mud suspension with a material containing non-metal oxides to produce the processed lime mud.

10. The method of claim 1 further comprising hydrating lime to form the suspension comprising calcium hydroxide.

11. The method of claim 1, wherein the carbonation step (b) causes PCC crystals to grow on processed lime mud clusters.

12. A method for producing a filler comprising precipitated calcium carbonate (PCC), the method comprising: (a) combining ingredients comprising calcium oxide and water to prepare a slurry comprising calcium hydroxide; (b) supplying processed lime mud to the slurry containing calcium hydroxide to form a resultant containing the processed lime mud and the calcium hydroxide; and (c) subjecting the resultant comprising the processed lime mud and the calcium hydroxide to a carbonation process to form a suspension comprising PCC.

13. The method of claim 12, wherein the precipitated calcium carbonate encapsulates processed lime mud clusters.

14. The method according to claim 12, wherein supplying the processed lime mud ends before the carbonation process begins.

15. The method according to claim 12, wherein performing the carbonation process comprises adding a material generating carbon dioxide to the resultant comprising the processed lime mud and the calcium hydroxide, and the method further comprises ending the supply of the processed lime mud to the slurry before adding the material generating carbon dioxide to the resultant.

16. The method of claim 12, wherein performing the carbonation process comprises adding a material that generates carbon dioxide to the resultant comprising the processed lime mud and the calcium hydroxide, and wherein supplying the processed lime mud continues during a portion of the carbonation process.

17. The method according to claim 12, wherein supplying the processed lime mud continues during the carbonation process and ends when or before the pH of the carbonation process reaches a value of 9 or 10.

18. The method according to claim 12, further comprising: (d) separating the precipitated calcium carbonate and processed white mud from the suspension; and (e) drying the separated solid to form a composite of dried precipitated calcium carbonate and processed lime mud.

19. The method of claim 12, wherein the method uses a total amount of processed lime mud in an amount of 0.3 wt% to 80 wt% based on the total weight of dry PCC to be prepared.

20. The method of claim 1, wherein the processed lime mud is produced by a method comprising: (a) providing an aqueous suspension of lime mud which is a by-product of alkali recovery in pulping and papermaking; (b) dewatering the lime mud suspension to produce dewatered lime mud solids; (c) washing the dewatered lime mud solids and producing a washed lime mud suspension; (d) screening the washed lime mud suspension to remove lime mud solids and / or grit particles of a selected size from the washed lime mud suspension; (e) grinding the sieved lime mud suspension; and (f) neutralizing the ground lime mud suspension with a material containing non-metal oxides to produce the processed lime mud.

21. The method according to claim 12, wherein the processed lime mud has a weight median diameter d of 0.3 μm to 10 μm. 50 .

22. A method for producing precipitated calcium carbonate, comprising: (a) hydrating calcium oxide to form slaked lime; (b) adding an aqueous suspension of processed white mud to the slaked lime; and (c) adding a material that generates carbon dioxide to form an aqueous suspension of precipitated calcium carbonate coated on the processed lime mud, wherein (i) the addition of the aqueous suspension of processed lime mud begins and ends before the addition of the carbon dioxide generating material begins, or (ii) the addition of the aqueous suspension of processed lime mud commences before the addition of the carbon dioxide generating material commences, continues during the addition of the carbon dioxide generating material, and ends when or before the pH of the reaction contents in step (c) reaches a value of 9 or 10, or (iii) adding the aqueous suspension of processed lime mud and adding the carbon dioxide generating material start simultaneously, and adding the aqueous suspension of processed lime mud ends when or before the pH of the reaction contents of step (c) reaches a value of 9 or 10.

23. The method according to claim 22, further comprising: (d) separating the precipitated calcium carbonate and processed white mud from the aqueous suspension; and (e) drying the separated solids to form a dry precipitated calcium carbonate at least partially coated on the processed lime mud.

24. The method according to claim 23, wherein the total amount of the processed lime mud used is greater than 0.3 wt% and less than 80 wt% based on the total weight of the dry precipitated calcium carbonate.

25. The method according to claim 22, wherein the processed lime mud has a weight median diameter d of 0.3 μm to 10 μm. 50 .

26. A paper product comprising precipitated calcium carbonate produced by the method according to any one of claims 1 to 25 and processed lime mud.

27. A filler material comprising precipitated calcium carbonate grown on processed lime mud particles produced by the method of any one of claims 1 to 25.

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