CA2355027A1 - Process for the production of water insoluble needle-shaped precipitated calcium sulphate dihydrate (caso4-2h2o) and its use as a filler in papermaking - Google Patents
Process for the production of water insoluble needle-shaped precipitated calcium sulphate dihydrate (caso4-2h2o) and its use as a filler in papermaking Download PDFInfo
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- CA2355027A1 CA2355027A1 CA 2355027 CA2355027A CA2355027A1 CA 2355027 A1 CA2355027 A1 CA 2355027A1 CA 2355027 CA2355027 CA 2355027 CA 2355027 A CA2355027 A CA 2355027A CA 2355027 A1 CA2355027 A1 CA 2355027A1
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- calcium sulphate
- calcium
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- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
- C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
- C09C1/02—Compounds of alkaline earth metals or magnesium
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F11/00—Compounds of calcium, strontium, or barium
- C01F11/46—Sulfates
- C01F11/466—Conversion of one form of calcium sulfate to another
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- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
- C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
- C09C1/02—Compounds of alkaline earth metals or magnesium
- C09C1/025—Calcium sulfates
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2004/00—Particle morphology
- C01P2004/10—Particle morphology extending in one dimension, e.g. needle-like
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2004/00—Particle morphology
- C01P2004/60—Particles characterised by their size
- C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/22—Rheological behaviour as dispersion, e.g. viscosity, sedimentation stability
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
- D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
- D21H17/63—Inorganic compounds
- D21H17/67—Water-insoluble compounds, e.g. fillers, pigments
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Life Sciences & Earth Sciences (AREA)
- Geology (AREA)
- Inorganic Chemistry (AREA)
- Paper (AREA)
- Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
Abstract
Needle shape calcium sulphate dehydrate (CaSO4.cndot.2H2O) filler particles were prepared by mixing freshly calcined calcium sulphate hemihydrate (CaSO4.cndot.1/2H2O) having an average particle size between 1 and 100 micrometers, and water in a reactor at high sheer with either no additives or together with acids or with calcium-or sulphate- containing additives. The average length and width of the produced filler particles were 5-35 micrometers and 1-5 micrometers respectively. The calcium sulphate dehydrate filler particles were then treated by a calcium chelating agent, perhaps followed by the addition of a weak acid. The mixture was then held at 90°C for 5-60min resulting in relatively water insoluble calcium sulphate dehydrate.
The filler suspension can be directly added to the pulp furnish before the paper sheet formation to obtain a high filler retention and improved optical properties with minimal filler losses due to solubility. The resulting filler did not cause any operating difficulties on the paper machine and provided, depending on the filler level, a 2-15%
decreased energy consumption in the drying section.
The filler suspension can be directly added to the pulp furnish before the paper sheet formation to obtain a high filler retention and improved optical properties with minimal filler losses due to solubility. The resulting filler did not cause any operating difficulties on the paper machine and provided, depending on the filler level, a 2-15%
decreased energy consumption in the drying section.
Description
Process for the producaion of water insoluble needle-shaped precipitated calcium sulphate dehydrate (CaS04~2H20) and its use as a filler in papermaking Field of Invention The present invention relates to the preparation and use of water insoluble calcium sulphate filler and the formation of the paper web using acid, neutral or alkaline conditions wherein calcium sulphate dehydrate is used as a filler.
Background of invention Fillers are inert, finely divided materials --- most commonly minerals - added to the papermaking furnish before the sheet formation. Their purpose is to fill spaces between cellulose fibers so as to improve the paper quality.
The potential advantage; of incorporating fillers include lower furnish cost, more efficient fiber resource use and improved optical and physical properties (printability, opacity, brightness, whiteness, softness, smoothness, etc).
However fillers may weaken paper by interfering with fiber-fiber bonding. Thus the possibility a!0 of increased pressroom breaks may limit the use of fillers.
In the past few decades, the use of mineral fillers in the paper industry has increased significantly. World consumption of pigments and fillers is forecasted to grow at an average rate of about 5% per annum during the period 1998-2003.
This fact in itself indicates their importance.
Several mineral fillers have been used in the paper industry. The most commonly-used mineral fillers are calcium carbonate, clay, titanium oxide and talc.
Typical level of filler addition ranged from 5 to 25% by weight.
Calcium sulphate forms can be ideal filler candidates in papermaking. They have excellent optical properties and their crystal form and crystal size can be modified easily. They are less expensive than wood fibers, therefore their partial substitution can also be economical.
The physical and chemical properties of calcium sulphate fillers are completely different from any other conventional filler. It has its own characteristics as a material, which must be bc.>rlue in mind.
The earliest applications involved to the use of ground calcium sulphate dehydrate and calcium sulphate anhydrate. Recently, attempts have been made to utilize precipitated tabular acicuhu- calcium sulphate dehydrate to obtain a high filler retention.
Calcium sulphate filler-.containing paper is reported to provide improved optical properties and a moderate strength loss. However, due to its high solubility, the losses are significant. During papermaking, a huge amount of filler is dissolved which increases the calcium and sulphate ion content of the whitewater and the effluent. This requires the whitewater and the effluent to be diluted between 2-5-fold 2 0 to avoid deposit formation and high calcium (hardness) and sulphate contamination of the system.
Brief description of the prior art ;?5 There are three different calcium sulfate forms: calcium sulfate dehydrate (CaS04~2H20), hemihydrate (CaS04~'/ZHZO) and anhydrite (CaS04). During the calcination of calcium sulfate dehydrate at 120-180°C, gypsum loses 1.5 mol of its crystal water and calcium sulfate hemihydrate is formed. When water is added to the hemihydrate, the hemihydrate binds the missing crystal water and crystallizes into dehydrate. Hemihydrate at high temperature loses its residual crystal water and forms S anhydrite. Anhydrite can not be converted back to hemihydrate or gypsum. At very high temperature anhydrate loses sulphur dioxide and oxygen and forms calcium-oxide.
CaS04~:ZH20 (dehydrate, gypsum) Water addition: Calcination at 120 - 180°C:
CaS04~0.5H20 + 1.SHzO -~ CaSOy2Hz0 CaS04~2H~0 -~ CaS04~0.5H20 + I.SHzO
CaSO,y0.5H20 (hemihydrate) 300-1180°C:
CaSOy0.5H20 --~ CaS04 + O.SHZO
CaS04 (anhydrate) 1180-1450°C:
CaS04 -~ Ca0 + SOz +'/20Z
C'a0 {calcium oxide) U.S. Patent 848,916 andl U.S. Patent 105,591 describe a method of adding l0 finely ground calcium sulphate dehydrate as filler for papermaking either in water or in sulphate-saturated water. The retention of the ground, round-shaped filler particles was low. The low filler retention together with the high solubility of calcium sulphate dehydrate (2400 mg/L), can not provide an economical filler for papermaking.
U.S. Patent 4,470,877 describes a method to improve calcium sulphate l5 retention. In the process large amount of polymeric resin latex binders and retention aids were needed for reasonable filler retention.
Background of invention Fillers are inert, finely divided materials --- most commonly minerals - added to the papermaking furnish before the sheet formation. Their purpose is to fill spaces between cellulose fibers so as to improve the paper quality.
The potential advantage; of incorporating fillers include lower furnish cost, more efficient fiber resource use and improved optical and physical properties (printability, opacity, brightness, whiteness, softness, smoothness, etc).
However fillers may weaken paper by interfering with fiber-fiber bonding. Thus the possibility a!0 of increased pressroom breaks may limit the use of fillers.
In the past few decades, the use of mineral fillers in the paper industry has increased significantly. World consumption of pigments and fillers is forecasted to grow at an average rate of about 5% per annum during the period 1998-2003.
This fact in itself indicates their importance.
Several mineral fillers have been used in the paper industry. The most commonly-used mineral fillers are calcium carbonate, clay, titanium oxide and talc.
Typical level of filler addition ranged from 5 to 25% by weight.
Calcium sulphate forms can be ideal filler candidates in papermaking. They have excellent optical properties and their crystal form and crystal size can be modified easily. They are less expensive than wood fibers, therefore their partial substitution can also be economical.
The physical and chemical properties of calcium sulphate fillers are completely different from any other conventional filler. It has its own characteristics as a material, which must be bc.>rlue in mind.
The earliest applications involved to the use of ground calcium sulphate dehydrate and calcium sulphate anhydrate. Recently, attempts have been made to utilize precipitated tabular acicuhu- calcium sulphate dehydrate to obtain a high filler retention.
Calcium sulphate filler-.containing paper is reported to provide improved optical properties and a moderate strength loss. However, due to its high solubility, the losses are significant. During papermaking, a huge amount of filler is dissolved which increases the calcium and sulphate ion content of the whitewater and the effluent. This requires the whitewater and the effluent to be diluted between 2-5-fold 2 0 to avoid deposit formation and high calcium (hardness) and sulphate contamination of the system.
Brief description of the prior art ;?5 There are three different calcium sulfate forms: calcium sulfate dehydrate (CaS04~2H20), hemihydrate (CaS04~'/ZHZO) and anhydrite (CaS04). During the calcination of calcium sulfate dehydrate at 120-180°C, gypsum loses 1.5 mol of its crystal water and calcium sulfate hemihydrate is formed. When water is added to the hemihydrate, the hemihydrate binds the missing crystal water and crystallizes into dehydrate. Hemihydrate at high temperature loses its residual crystal water and forms S anhydrite. Anhydrite can not be converted back to hemihydrate or gypsum. At very high temperature anhydrate loses sulphur dioxide and oxygen and forms calcium-oxide.
CaS04~:ZH20 (dehydrate, gypsum) Water addition: Calcination at 120 - 180°C:
CaS04~0.5H20 + 1.SHzO -~ CaSOy2Hz0 CaS04~2H~0 -~ CaS04~0.5H20 + I.SHzO
CaSO,y0.5H20 (hemihydrate) 300-1180°C:
CaSOy0.5H20 --~ CaS04 + O.SHZO
CaS04 (anhydrate) 1180-1450°C:
CaS04 -~ Ca0 + SOz +'/20Z
C'a0 {calcium oxide) U.S. Patent 848,916 andl U.S. Patent 105,591 describe a method of adding l0 finely ground calcium sulphate dehydrate as filler for papermaking either in water or in sulphate-saturated water. The retention of the ground, round-shaped filler particles was low. The low filler retention together with the high solubility of calcium sulphate dehydrate (2400 mg/L), can not provide an economical filler for papermaking.
U.S. Patent 4,470,877 describes a method to improve calcium sulphate l5 retention. In the process large amount of polymeric resin latex binders and retention aids were needed for reasonable filler retention.
U.S. Patent 2,304,361 describes a process for making the calcium sulphate dehydrate filler using dilution water from the paper machine. This led to very small needle-shaped crystals. The slurry was then fed to the machine without dewatering or drying the gypsum.
U.S. Patent 4,152,408 describes a method to produce fibrous calcium sulphate by autoclaving a dilute aqueous suspension of gypsum. L1.S. Patent 4,270,954 describes a method to produce inorganic fibers based on calcium sulphate dehydrate or calcium sulphate aluminate hydrate. The average ratio of length to diameter of the fibers was about 100:1 and the length of the fibers is at least 0.2 mm.
Canadian Patent 1,307,9C13 describes a process to make tabular acicular gypsum filler having an aspect ration of 100:10:1 and average length in the longest dimension of about 100-450 micrometers. Because of the shape of the particles, high filler retention can be obtained. However, the large filler particles can yield weak bonding in the paper web which can possibly result in Tinting in the pressroom.
I 5 European Patent 0,056,200 describes a method of making elongated crystals of calcium sulphate dehydrate from calcium sulphate hemihydrate separately or together with a salt of aluminium such as aluminium sulphate. A continuous preparation of the filler particles is described, however the filler losses on the paper machine due to solubility should be high.
~!0 From the above it is apparent that a high filler retention in the paper is a must and there is a need for reducing the size and the solubility of the particles.
Our first objective is to produce needle-shaped calcium sulphate dehydrate particles with an appropriate particle size ( 1-3 micrometers x 5-25 micrometers) for papermaking. This size range provides reasonable filler retention, good bonding in the 25 sheet and less tinting problem in the pressroom.
U.S. Patent 4,152,408 describes a method to produce fibrous calcium sulphate by autoclaving a dilute aqueous suspension of gypsum. L1.S. Patent 4,270,954 describes a method to produce inorganic fibers based on calcium sulphate dehydrate or calcium sulphate aluminate hydrate. The average ratio of length to diameter of the fibers was about 100:1 and the length of the fibers is at least 0.2 mm.
Canadian Patent 1,307,9C13 describes a process to make tabular acicular gypsum filler having an aspect ration of 100:10:1 and average length in the longest dimension of about 100-450 micrometers. Because of the shape of the particles, high filler retention can be obtained. However, the large filler particles can yield weak bonding in the paper web which can possibly result in Tinting in the pressroom.
I 5 European Patent 0,056,200 describes a method of making elongated crystals of calcium sulphate dehydrate from calcium sulphate hemihydrate separately or together with a salt of aluminium such as aluminium sulphate. A continuous preparation of the filler particles is described, however the filler losses on the paper machine due to solubility should be high.
~!0 From the above it is apparent that a high filler retention in the paper is a must and there is a need for reducing the size and the solubility of the particles.
Our first objective is to produce needle-shaped calcium sulphate dehydrate particles with an appropriate particle size ( 1-3 micrometers x 5-25 micrometers) for papermaking. This size range provides reasonable filler retention, good bonding in the 25 sheet and less tinting problem in the pressroom.
Our second objective is to reduce the solubility rate and the solubility of the produced calcium sulphate dehydrate filler in a simple, fast and economical way.
Brief description of the drawin;is Figure la: The schematic diagram of the system producing needle-shaped calcium sulphate dehydrate filler. (1) calcium sulphate hemihydrate storage tank; (2) mixing tank; (3) agitator; (4) heater; (5) pH, temperature, conductivity and calcium sensors;
(6) calcium sulphate dehydrate storage tank.
CaSO~ ~ ~/2 H2O
Brief description of the drawin;is Figure la: The schematic diagram of the system producing needle-shaped calcium sulphate dehydrate filler. (1) calcium sulphate hemihydrate storage tank; (2) mixing tank; (3) agitator; (4) heater; (5) pH, temperature, conductivity and calcium sensors;
(6) calcium sulphate dehydrate storage tank.
CaSO~ ~ ~/2 H2O
5 - 25°l0 1 10 - 50°C
200 - 2000rpm Figure 1b: The schematic diagram of the system producing needle-shaped calcium sulphate dihydrate filler. (1) mixing tank; (2) agitator; (3) heater; (4) computer controlled valves; (5) storage tank.
CaSC4 ~ 2 H2c~
suspension fresh or process water chelating ~~"~ i~ 2~, papermachine agent aciti - 25%
20 - 90°C
high sheer 1.. ) Description of the preferred embodiments Nowadays there is no mill in the world using natural, ground gypsum as filler l 0 because of its high impurities content, low brightness and particle fineness, excessive solubility, small specific surface area and poor retention.
The filler of the present invention is prepared by precipitating calcium sulphate hemihydrate in a continuously stirred atmospheric pressure reactor at medium-high sheer between 10"(_' and 50°C temperature. Since the solubility of the calcium sulphate hemihydrate is. higher then the solubility of the calcium sulphate dehydrate, the hemihydrate slurry with its low levels of supersaturation provides an excellent medium for the calcium sulphate dehydrate formation.
Freshly calcined calcium sulphate hemihydrate with an average particle size of 1 - 100 micrometers was found to be the best reactant for our purpose. The hemihydrate was added to the mixing tank between 5°,~o and 25%
consistency at a temperature between 10°C and SO"C, with agitation between 200rpm and 2000rpm.
The conversion from calcium sulphate hemihydrate to calcium sulphate dehydrate with no additives was completed in about 20-60 minutes. The conversion can be accelerated, and the particle size can be modified by using acids -such as sulphuric acid and hydrochloriic acid, and/or by using calcium or sulphate or aluminium containing additives - such as calcium-chloride and aluminium sulphate, and/or by adding small amount of fines or pulp to the mixture. The average length and width of the produced filler particles are 5-3~ micrometers and 1-5 micrometers respectively.
Calcium sulphate dehydrate is the most stable form of calcium sulphate. It cannot bind any more crystal water, so its water slurry does not harden. Since the solubility of calcium sulphate dehydrate does not change between pH=5 and pH=9 and temperature between 10"C and SO"C, the calcium sulphate dehydrate slurry can be 2 0 stored and transported without agitation. The produced calcium sulphate dehydrate filler can be directly added to flue papermaking furnish with relatively high retention or can be treated by further additives and heat to produce water insoluble calcium sulphate dehydrate.
To produce water insoluble calcium sulphate hemihydrate, the calcium sulphate dehydrate filler should be treated by a calcium chelating agent with or without the following addition of a weak acid at higher temperature.
The calcium chelating a~,ent together with the excess calcium ion content of the slurry form an insoluble layer on the surface of the filler particles.
This layer helps to reduce the solubility of the surface of the calcium sulphate dehydrate. The calcium chelating agent can be condensed phosphate such as sodium-hexametaphosphate or sodium-tripolyphosphate.
Following the addition of the chelating agent, a weak acid can be added to the system such as phosphoric acid, or hexametaphosphoric acid.
Water insoluble calcium sulphate dehydrate can be formed by mixing the calcium sulphate dehydrate filler with calcium chelating agent at concentration ranging from about 0.01 to 5 weight percent of the dry filler without or with a weak acid at concentration ranging from about 0.01 to 5 weight percent of the dry filler.
The mixture then should. be held at 30-90°C for 5-60min resulting in water insoluble calcium sulphate dehydrate.
The filler suspension tlae~~ can be directly added to pulp furnish (wood-free or wood containing; acid, neutral or alkaline) before paper formation to obtain high filler retention, minimal filler losses due solubility and improved optical properties.
f.0 Experiment 1.
Preparation of the calciunn sulplrczte dihydrczte feller without additives In a series of evaluation calcium sulphate hemihydrate and water were fed to a ~5 mixing tank without additives at different levels of concentration, agitation and temperature (Table l, Sample 1-~3~. The schematic diagram of the system is shown in Figure la. The system consists a calcium sulphate hemihydrate storage tank (1.); a mixing tank (2); two agitators (3); a heater (4); pH, temperature, conductivity and calcium sensors (5); and a calcium sulphate dehydrate storage tank (6).
Freshly calcined calcium sulphate hemihydrate was used for the experiments.
The average particle size of the calcium sulphate hemihydrate was between 0.1 and 10 micrometers. The concentration of the calcium sulphate hemihydrate in the suspension varied between 5% and 25'%.
In this experiment deionised water, tap water and process water were used.
In the first part of the experiment - Sample l, Sample 2, Sample 3 - the effect of using deionised water, tap water and process water was compared. No difference was found between using deionised or tap water. The conversion can be completed in the same time, and the particle size of the calcium sulphate dehydrate was identical.
Using process water accelerated the conversion and made the particles somewhat bigger. This can be explained by the presence of fines. Those fines in the process water acted as nucleus for the cy stal formation process.
Sample 4 and Sample 5 the calcium sulphate dehydrate filler was prepared in tap water at lower consistency. The lower the concentration the slower the conversion from calcium sulphate hemihydrate to calcium sulphate dehydrate, but the particle size of the filler particles were the same.
Table l: Experiment 1 Agitation FillerFiller Sample ConsistencyWater TemperatureConversion speed lengthwidth Nr. [%] typo [C] time [min]
[rpm] [pm] [pm]
deionised ', water -2 10 tap 20 20 10-20 1-2 water 800 !
process 3 10 e 800 14 15-20 1-2 water 4 7.5 tap 800 ~ 23 15-20 1-2 water 20 __ 5 tap 800 ( 25 15-20 1-2 water 20 6 10 tap 600 e 24 10-20 2-3 water 20 I
200 - 2000rpm Figure 1b: The schematic diagram of the system producing needle-shaped calcium sulphate dihydrate filler. (1) mixing tank; (2) agitator; (3) heater; (4) computer controlled valves; (5) storage tank.
CaSC4 ~ 2 H2c~
suspension fresh or process water chelating ~~"~ i~ 2~, papermachine agent aciti - 25%
20 - 90°C
high sheer 1.. ) Description of the preferred embodiments Nowadays there is no mill in the world using natural, ground gypsum as filler l 0 because of its high impurities content, low brightness and particle fineness, excessive solubility, small specific surface area and poor retention.
The filler of the present invention is prepared by precipitating calcium sulphate hemihydrate in a continuously stirred atmospheric pressure reactor at medium-high sheer between 10"(_' and 50°C temperature. Since the solubility of the calcium sulphate hemihydrate is. higher then the solubility of the calcium sulphate dehydrate, the hemihydrate slurry with its low levels of supersaturation provides an excellent medium for the calcium sulphate dehydrate formation.
Freshly calcined calcium sulphate hemihydrate with an average particle size of 1 - 100 micrometers was found to be the best reactant for our purpose. The hemihydrate was added to the mixing tank between 5°,~o and 25%
consistency at a temperature between 10°C and SO"C, with agitation between 200rpm and 2000rpm.
The conversion from calcium sulphate hemihydrate to calcium sulphate dehydrate with no additives was completed in about 20-60 minutes. The conversion can be accelerated, and the particle size can be modified by using acids -such as sulphuric acid and hydrochloriic acid, and/or by using calcium or sulphate or aluminium containing additives - such as calcium-chloride and aluminium sulphate, and/or by adding small amount of fines or pulp to the mixture. The average length and width of the produced filler particles are 5-3~ micrometers and 1-5 micrometers respectively.
Calcium sulphate dehydrate is the most stable form of calcium sulphate. It cannot bind any more crystal water, so its water slurry does not harden. Since the solubility of calcium sulphate dehydrate does not change between pH=5 and pH=9 and temperature between 10"C and SO"C, the calcium sulphate dehydrate slurry can be 2 0 stored and transported without agitation. The produced calcium sulphate dehydrate filler can be directly added to flue papermaking furnish with relatively high retention or can be treated by further additives and heat to produce water insoluble calcium sulphate dehydrate.
To produce water insoluble calcium sulphate hemihydrate, the calcium sulphate dehydrate filler should be treated by a calcium chelating agent with or without the following addition of a weak acid at higher temperature.
The calcium chelating a~,ent together with the excess calcium ion content of the slurry form an insoluble layer on the surface of the filler particles.
This layer helps to reduce the solubility of the surface of the calcium sulphate dehydrate. The calcium chelating agent can be condensed phosphate such as sodium-hexametaphosphate or sodium-tripolyphosphate.
Following the addition of the chelating agent, a weak acid can be added to the system such as phosphoric acid, or hexametaphosphoric acid.
Water insoluble calcium sulphate dehydrate can be formed by mixing the calcium sulphate dehydrate filler with calcium chelating agent at concentration ranging from about 0.01 to 5 weight percent of the dry filler without or with a weak acid at concentration ranging from about 0.01 to 5 weight percent of the dry filler.
The mixture then should. be held at 30-90°C for 5-60min resulting in water insoluble calcium sulphate dehydrate.
The filler suspension tlae~~ can be directly added to pulp furnish (wood-free or wood containing; acid, neutral or alkaline) before paper formation to obtain high filler retention, minimal filler losses due solubility and improved optical properties.
f.0 Experiment 1.
Preparation of the calciunn sulplrczte dihydrczte feller without additives In a series of evaluation calcium sulphate hemihydrate and water were fed to a ~5 mixing tank without additives at different levels of concentration, agitation and temperature (Table l, Sample 1-~3~. The schematic diagram of the system is shown in Figure la. The system consists a calcium sulphate hemihydrate storage tank (1.); a mixing tank (2); two agitators (3); a heater (4); pH, temperature, conductivity and calcium sensors (5); and a calcium sulphate dehydrate storage tank (6).
Freshly calcined calcium sulphate hemihydrate was used for the experiments.
The average particle size of the calcium sulphate hemihydrate was between 0.1 and 10 micrometers. The concentration of the calcium sulphate hemihydrate in the suspension varied between 5% and 25'%.
In this experiment deionised water, tap water and process water were used.
In the first part of the experiment - Sample l, Sample 2, Sample 3 - the effect of using deionised water, tap water and process water was compared. No difference was found between using deionised or tap water. The conversion can be completed in the same time, and the particle size of the calcium sulphate dehydrate was identical.
Using process water accelerated the conversion and made the particles somewhat bigger. This can be explained by the presence of fines. Those fines in the process water acted as nucleus for the cy stal formation process.
Sample 4 and Sample 5 the calcium sulphate dehydrate filler was prepared in tap water at lower consistency. The lower the concentration the slower the conversion from calcium sulphate hemihydrate to calcium sulphate dehydrate, but the particle size of the filler particles were the same.
Table l: Experiment 1 Agitation FillerFiller Sample ConsistencyWater TemperatureConversion speed lengthwidth Nr. [%] typo [C] time [min]
[rpm] [pm] [pm]
deionised ', water -2 10 tap 20 20 10-20 1-2 water 800 !
process 3 10 e 800 14 15-20 1-2 water 4 7.5 tap 800 ~ 23 15-20 1-2 water 20 __ 5 tap 800 ( 25 15-20 1-2 water 20 6 10 tap 600 e 24 10-20 2-3 water 20 I
7 10 tap 400 e 30 10-20 2-3 water 20 I
~
~
8 10 tap I 50 21 10-20 1-3 water 800 ~
e '__ Sample 6 and Sample 7 the calcium sulphate dehydrate filler were prepared in tap water with slower agitation. The moderate agitation led to slower conversion from 5 calcium sulphate hemihydrate bo calcium sulphate dehydrate and somewhat thicker crystals.
Sample 8 the calcium sulphate dehydrate filler was prepared at higher temperature. No significant changes was observed either in conversion time or particle size, compared to lower temperatures.
to Experiment 2.
Preparation of the calcium sulphate dehydrate fcller with additives In a series of evaluation calcium sulphate hemihydrate and water were fed to a mixing tank with additives at difiFerent levels of concentration (Table 2, Sample 9-15).
The schematic diagram of the system is shown in Figure la. The same system was used as for Experiment 1.
Freshly calcined calcium sulphate hemihydrate was used for the experiments.
The average particle sire of the calcium sulphate hemihydrate was between 1 and 100 micrometers. The concentration of the calcium sulphate hemihydrate was 10%. In this experiment tap water, 800rpm agitation speed were used. The mixture was thermostated at 20°C.
In the first part of the experiment --- Sample 9, Sample 10 - the effect of acids on the calcium sulphate dehydrate formation was investigated. Both hydrochloric and sulphuric acid made the precipit~~tion faster. Sulphuric acid increased the sulphate ion content and the super saturation of the calcium sulphate in the system resulting in faster precipitation than with hydrochloric acid.
In the second part of the ~: xperiment - Sample 11, Sample 12, Sample 13 - the effect of using calcium containing, sulphate containing and aluminium containing salts was investigated. All three additives resulted in faster precipitation, the calcium chloride and aluminium sulphate due to increased super saturation, the aluminium chloride due to its acidic character°istic.
Sample 14 and Sample 15 the effect of fines and pulp on the crystal formation was investigated. Botl1 resulted faster precipitation and somewhat bigger particles.
This means process water -- white water - can be used for the precipitation, which can also reduce the water consumption of papermaking.
fable 2: Experiment 2 FillerFiller SampleConsistency ConcentrationConversion Additive lengthwidth Nr. [%] ' ['%] time [min]
[pm] [pm]
e '__ Sample 6 and Sample 7 the calcium sulphate dehydrate filler were prepared in tap water with slower agitation. The moderate agitation led to slower conversion from 5 calcium sulphate hemihydrate bo calcium sulphate dehydrate and somewhat thicker crystals.
Sample 8 the calcium sulphate dehydrate filler was prepared at higher temperature. No significant changes was observed either in conversion time or particle size, compared to lower temperatures.
to Experiment 2.
Preparation of the calcium sulphate dehydrate fcller with additives In a series of evaluation calcium sulphate hemihydrate and water were fed to a mixing tank with additives at difiFerent levels of concentration (Table 2, Sample 9-15).
The schematic diagram of the system is shown in Figure la. The same system was used as for Experiment 1.
Freshly calcined calcium sulphate hemihydrate was used for the experiments.
The average particle sire of the calcium sulphate hemihydrate was between 1 and 100 micrometers. The concentration of the calcium sulphate hemihydrate was 10%. In this experiment tap water, 800rpm agitation speed were used. The mixture was thermostated at 20°C.
In the first part of the experiment --- Sample 9, Sample 10 - the effect of acids on the calcium sulphate dehydrate formation was investigated. Both hydrochloric and sulphuric acid made the precipit~~tion faster. Sulphuric acid increased the sulphate ion content and the super saturation of the calcium sulphate in the system resulting in faster precipitation than with hydrochloric acid.
In the second part of the ~: xperiment - Sample 11, Sample 12, Sample 13 - the effect of using calcium containing, sulphate containing and aluminium containing salts was investigated. All three additives resulted in faster precipitation, the calcium chloride and aluminium sulphate due to increased super saturation, the aluminium chloride due to its acidic character°istic.
Sample 14 and Sample 15 the effect of fines and pulp on the crystal formation was investigated. Botl1 resulted faster precipitation and somewhat bigger particles.
This means process water -- white water - can be used for the precipitation, which can also reduce the water consumption of papermaking.
fable 2: Experiment 2 FillerFiller SampleConsistency ConcentrationConversion Additive lengthwidth Nr. [%] ' ['%] time [min]
[pm] [pm]
9 10 ~ H~S~Oa 1 ~ 16 15-25 1-3 ~
10 HC'l 2 18 10-20 1-2 11 10 CaC,'l, 1 15 15-25 1-3 12 10 ~ AIZ(S~Oa)3 1 15 15-25 1-3 13 10 A1C'l~ 1 18 10-20 1-2 ~
i ~ I
i ~ I
14 10 finca 0.3 11 15-25 j 10 pulp 0.3 13 15-25 1-3 Experiment 3.
Effect of the chelating cagerct on the solubilitv of the calcium sulphate dihydYate filler l.0 A calcium chelating agent was added to the calcium sulphate dihydrate slurry produced from freshly calcined calcium sulphate hemihydrate according to Experiment 1, Sample 1. The mixture was agitated at high sheer without or with the presence of a weak acid for short period of time. Then the solubility of calcium sulphate was measured. The schematic diagram of the system is shown in Figure 1b.
For Sample 16, SOOg of calcium sulphate dehydrate slurry was prepared according to Experiment 1, Sample 1. The mixture was thermostated at 20°C for 15 minutes. The solubility of calcium sulphate was measured and found to be 2400 mg/L. This value was in good agreement with the literature value.
For Sample 17, 500g of calcium sulphate dehydrate slurry was prepared according to Experiment l, Sarr~ple 1. Following the preparation 0.5-5% of sodium hexametaphosphate, based on calcium sulphate dehydrate, was added to the slurry, at 20°C and the mixture was agitated for 15 minutes. The solubility of the treated calcium sulphate dehydrate was measured. Results are summarized in Figure 2.
Increasing sodium hexametaphosphate concentration gave decreased solubility. The curve is a saturation type curve, above a certain threshold -about 3%
of sodium hexametaphosphate -- the excess of sodium hexametaphosphate did not decrease the solubility any more.
Figure 2. Solubility of calcium sulphate dehydrate after treating by sodium hexametaphosphate and phosphoric acid at 20°C
~0% H3P04 2100 ~ 1% H3P04 ~~ 2% H3P04 X3% H3P04 p4% H3P04 5% H3P04 f (I\1aP03)~ content [%]
For Sample 18, SOOg of calcium sulphate dehydrate slurry was prepared according to Experiment l, Sample 1. Following the preparation 0.5-5% of sodium hexametaphosphate, based on calcium sulphate dehydrate, was added to the slurry, followed by the addition of 1-5% phosphoric acid, based on calcium sulphate J.0 dehydrate, at 20°C and the mixture was agitated for 15 minutes.
Results are summarized in Figure 2.
From Figure 2, it can be seen, that 1 % sodium hexametaphosphate, based on calcium sulphate dehydrate, together with 2'% phosphoric acid, based on calcium sulphate dehydrate, reduced the solubility of the calcium sulphate dehydrate by about l5 25%. It was found, that at low sodium hexametaphosphate concentration the effect of using phosphoric acid on the solubility of calcium sulphate dehydrate can be significant, however at higher levels of concentration of sodium hexametaphosphate the use of phosphoric acid was unnecessary.
Experiment 4.
Effect of the chelcrting agent on .the solubility of the calcium sulphate dehydrate filler at different temperaturE:~
For Sample 19, SOOg of' calcium sulphate dehydrate slurry was prepared according to Experiment 1, Sample 1. Following the preparation 0.5-5% of sodium hexametaphosphate, based on calcium sulphate dehydrate, was added to the slurry.
Following the additions, the mixture was thermostated between 60°C and 85°C and agitated for 30 minutes. The solubility of the treated calcium sulphate dehydrate was then measured. Results are summarized in Figure 3. The schematic diagram of the system is shown in Figure 1 b. The same system was used as for Experiment 3.
Increasing temperature and increasing concentration of sodium hexametaphosphate gave decreased solubility. The solubility curve of calcium sulphate dehydrate at 60°C and at 85°C was also a saturation type curve. Above 3% of sodium hexametaphosphate, based on calcium sulphate dehydrate the solubility of f.0 calcium sulphate dehydrate did not decrease any more. Using 2% sodium hexametaphosphate, based on calcium sulphate dehydrate and 60°C the solubility of the calcium sulphate dehydrate decreased by about 30'%. Increasing the temperature from 60°C to 85°C did not make any difference in the solubility of calcium sulphate dehydrate.
For Sample 20, SOOg of calcium sulphate dehydrate slurry was prepared according to Experiment 1, Sample 1. Following the preparation 0.5-5% of sodium hexametaphosphate, based on calcium sulphate dehydrate, was added to the slurry, followed by the addition of 1 °/~ phosphoric acid, based on calcium sulphate dehydrate.
Following the additions, the mixture was thermostated between 60°C and agitated for 30 minutes. The solubility of the treated calcium sulphate dehydrate was then measured. Results are summarized in Figure 3.
Figure 3. Solubility of calcium sulphate dehydrate after treating by sodium hexametaphosphate at different temperature 2500 _ ~ no H3P04 at 20°C
1900 ono H3P04 at 60°C
~_ ;~= no H3P04 at 85°C
X 1%~ H3P04 at 60°C
(NaP03)~, content [%]
From Figure 3, it can be seen, that 1 % sodium hexametaphosphate, based on l 5 calcium sulphate dehydrate, together with 1 % phosphoric acid, based on calcium sulphate dehydrate, reduced the solubility of the calcium sulphate dehydrate by about 40%. It was found, that at low sodium hexametaphosphate concentration -between 0.5 and 2%, based on calcium sulphate dehydrate - the effect of using phosphoric acid on the solubility of calcium sulphate dehydrate can be significant, however at higher levels of concentration of sodium hexametaphosphate the use of phosphoric acid was unnecessary.
Experiment 5.
Effect of the chelating agent on solubility of the calcium sulphate dehydrate filler For Sample 21, SOOg of calcium sulphate dehydrate slurry was prepared according to Experiment l, Sample 8 at 50°C. Following the preparation immediately 0.2-5% of sodium hexametaphosphate, based on calcium sulphate dehydrate, was added to the slurry which was still thermostated at 50°C. The slurry was agitated for 5-15 minutes. The solubility of the treated calcium sulphate dehydrate was then measured. Results are summarized in Figure 4. The schematic diagram of the system is shown in Figure 1 b. The same system was used as for Experiment 3. and Experiment 4.
Using sodium hexametaphosphate at these conditions resulted dramatic solubility reduction. 2% and 5~'/~ of sodium hexametaphosphate, based on calcium sulphate dehydrate, decreased thc: solubility of calcium sulphate dehydrate by 60% and 70% respectively. Increasing sodium hexametaphosphate concentration gave decreased solubility. The curve was also a saturation type curve. The effect of time at high sodium hexametaphosphate~ concentration seems to be important.
For Sample 22, SOOg of calcium sulphate dehydrate slurry was prepared according to Experiment l, Sample 8 at 50°C. Following the preparation 0.2-5% of sodium hexametaphosphate, based on calcium sulphate dehydrate, was added to the slurry, followed by the addition of 1-2% phosphoric acid, based on calcium sulphate dehydrate. The slurry was then~nostated at 50°C. The slu rry was agitated for 5-15 minutes. The solubility of~ the trf:ated calcium sulphate dehydrate was then measured.
Results are summarized in Figure 4.
From Figure 4, it can be seen, that in the 0.2% to 1% sodium hexametaphosphate concentration range the presence of phosphoric acid slightly decreased the solubility of calcium sulphate dehydrate. However, above that concentration range the phosphor~ic acid made the treatment worse.
Figure 4. Solubility of calcium sulphate dihydrate after treating by sodium hexametaphosphate at high temperature Solubility of gypsum after treatment ~ no H3P04 5 min I no H3P04 15 min 1500 1i ~ 1% H3P04 5 min a I % H3P04 15 min ', 2% H3P04 5 min 0 1000 ~ 2% H3P04 15 min (7 1 2 3 4 5 G
(NaP03)c, ~%]
Effect of the chelating cagerct on the solubilitv of the calcium sulphate dihydYate filler l.0 A calcium chelating agent was added to the calcium sulphate dihydrate slurry produced from freshly calcined calcium sulphate hemihydrate according to Experiment 1, Sample 1. The mixture was agitated at high sheer without or with the presence of a weak acid for short period of time. Then the solubility of calcium sulphate was measured. The schematic diagram of the system is shown in Figure 1b.
For Sample 16, SOOg of calcium sulphate dehydrate slurry was prepared according to Experiment 1, Sample 1. The mixture was thermostated at 20°C for 15 minutes. The solubility of calcium sulphate was measured and found to be 2400 mg/L. This value was in good agreement with the literature value.
For Sample 17, 500g of calcium sulphate dehydrate slurry was prepared according to Experiment l, Sarr~ple 1. Following the preparation 0.5-5% of sodium hexametaphosphate, based on calcium sulphate dehydrate, was added to the slurry, at 20°C and the mixture was agitated for 15 minutes. The solubility of the treated calcium sulphate dehydrate was measured. Results are summarized in Figure 2.
Increasing sodium hexametaphosphate concentration gave decreased solubility. The curve is a saturation type curve, above a certain threshold -about 3%
of sodium hexametaphosphate -- the excess of sodium hexametaphosphate did not decrease the solubility any more.
Figure 2. Solubility of calcium sulphate dehydrate after treating by sodium hexametaphosphate and phosphoric acid at 20°C
~0% H3P04 2100 ~ 1% H3P04 ~~ 2% H3P04 X3% H3P04 p4% H3P04 5% H3P04 f (I\1aP03)~ content [%]
For Sample 18, SOOg of calcium sulphate dehydrate slurry was prepared according to Experiment l, Sample 1. Following the preparation 0.5-5% of sodium hexametaphosphate, based on calcium sulphate dehydrate, was added to the slurry, followed by the addition of 1-5% phosphoric acid, based on calcium sulphate J.0 dehydrate, at 20°C and the mixture was agitated for 15 minutes.
Results are summarized in Figure 2.
From Figure 2, it can be seen, that 1 % sodium hexametaphosphate, based on calcium sulphate dehydrate, together with 2'% phosphoric acid, based on calcium sulphate dehydrate, reduced the solubility of the calcium sulphate dehydrate by about l5 25%. It was found, that at low sodium hexametaphosphate concentration the effect of using phosphoric acid on the solubility of calcium sulphate dehydrate can be significant, however at higher levels of concentration of sodium hexametaphosphate the use of phosphoric acid was unnecessary.
Experiment 4.
Effect of the chelcrting agent on .the solubility of the calcium sulphate dehydrate filler at different temperaturE:~
For Sample 19, SOOg of' calcium sulphate dehydrate slurry was prepared according to Experiment 1, Sample 1. Following the preparation 0.5-5% of sodium hexametaphosphate, based on calcium sulphate dehydrate, was added to the slurry.
Following the additions, the mixture was thermostated between 60°C and 85°C and agitated for 30 minutes. The solubility of the treated calcium sulphate dehydrate was then measured. Results are summarized in Figure 3. The schematic diagram of the system is shown in Figure 1 b. The same system was used as for Experiment 3.
Increasing temperature and increasing concentration of sodium hexametaphosphate gave decreased solubility. The solubility curve of calcium sulphate dehydrate at 60°C and at 85°C was also a saturation type curve. Above 3% of sodium hexametaphosphate, based on calcium sulphate dehydrate the solubility of f.0 calcium sulphate dehydrate did not decrease any more. Using 2% sodium hexametaphosphate, based on calcium sulphate dehydrate and 60°C the solubility of the calcium sulphate dehydrate decreased by about 30'%. Increasing the temperature from 60°C to 85°C did not make any difference in the solubility of calcium sulphate dehydrate.
For Sample 20, SOOg of calcium sulphate dehydrate slurry was prepared according to Experiment 1, Sample 1. Following the preparation 0.5-5% of sodium hexametaphosphate, based on calcium sulphate dehydrate, was added to the slurry, followed by the addition of 1 °/~ phosphoric acid, based on calcium sulphate dehydrate.
Following the additions, the mixture was thermostated between 60°C and agitated for 30 minutes. The solubility of the treated calcium sulphate dehydrate was then measured. Results are summarized in Figure 3.
Figure 3. Solubility of calcium sulphate dehydrate after treating by sodium hexametaphosphate at different temperature 2500 _ ~ no H3P04 at 20°C
1900 ono H3P04 at 60°C
~_ ;~= no H3P04 at 85°C
X 1%~ H3P04 at 60°C
(NaP03)~, content [%]
From Figure 3, it can be seen, that 1 % sodium hexametaphosphate, based on l 5 calcium sulphate dehydrate, together with 1 % phosphoric acid, based on calcium sulphate dehydrate, reduced the solubility of the calcium sulphate dehydrate by about 40%. It was found, that at low sodium hexametaphosphate concentration -between 0.5 and 2%, based on calcium sulphate dehydrate - the effect of using phosphoric acid on the solubility of calcium sulphate dehydrate can be significant, however at higher levels of concentration of sodium hexametaphosphate the use of phosphoric acid was unnecessary.
Experiment 5.
Effect of the chelating agent on solubility of the calcium sulphate dehydrate filler For Sample 21, SOOg of calcium sulphate dehydrate slurry was prepared according to Experiment l, Sample 8 at 50°C. Following the preparation immediately 0.2-5% of sodium hexametaphosphate, based on calcium sulphate dehydrate, was added to the slurry which was still thermostated at 50°C. The slurry was agitated for 5-15 minutes. The solubility of the treated calcium sulphate dehydrate was then measured. Results are summarized in Figure 4. The schematic diagram of the system is shown in Figure 1 b. The same system was used as for Experiment 3. and Experiment 4.
Using sodium hexametaphosphate at these conditions resulted dramatic solubility reduction. 2% and 5~'/~ of sodium hexametaphosphate, based on calcium sulphate dehydrate, decreased thc: solubility of calcium sulphate dehydrate by 60% and 70% respectively. Increasing sodium hexametaphosphate concentration gave decreased solubility. The curve was also a saturation type curve. The effect of time at high sodium hexametaphosphate~ concentration seems to be important.
For Sample 22, SOOg of calcium sulphate dehydrate slurry was prepared according to Experiment l, Sample 8 at 50°C. Following the preparation 0.2-5% of sodium hexametaphosphate, based on calcium sulphate dehydrate, was added to the slurry, followed by the addition of 1-2% phosphoric acid, based on calcium sulphate dehydrate. The slurry was then~nostated at 50°C. The slu rry was agitated for 5-15 minutes. The solubility of~ the trf:ated calcium sulphate dehydrate was then measured.
Results are summarized in Figure 4.
From Figure 4, it can be seen, that in the 0.2% to 1% sodium hexametaphosphate concentration range the presence of phosphoric acid slightly decreased the solubility of calcium sulphate dehydrate. However, above that concentration range the phosphor~ic acid made the treatment worse.
Figure 4. Solubility of calcium sulphate dihydrate after treating by sodium hexametaphosphate at high temperature Solubility of gypsum after treatment ~ no H3P04 5 min I no H3P04 15 min 1500 1i ~ 1% H3P04 5 min a I % H3P04 15 min ', 2% H3P04 5 min 0 1000 ~ 2% H3P04 15 min (7 1 2 3 4 5 G
(NaP03)c, ~%]
Claims (61)
1. A method for making needle shape calcium sulphate dihydrate crystals as filler for papermaking, by mixing calcium sulphate hemihydrate with water at different levels of concentration, at different levels agitation, at different temperature with or without acids and/or calcium containing and/or sulphate containing and/or aluminium containing salts.
2. A method as defined in Claim 1, wherein said calcium sulphate hemihydrate is calcined from natural gypsum.
3. A method as defined in Claim 1, wherein said calcium sulphate hemihydrate is calcined from by-product gypsum.
4. A method as defined in Claim 1, wherein said calcium sulphate hemihydrate is having an average particle size between 1 micrometers and 100 micrometers.
5. A method as defined in Claim 1, wherein said different levels of agitation is between 100rpm and 3000rpm.
6. A method as defined in Claim 1, wherein the time of agitation is between 10min and 60min.
7. A method as defined in Claim 1, wherein said different temperature is between 10°C and 80°C.
8. A method as defined in Claim 1, wherein said acid is sulphuric acid H2SO4.
9. A method as defined in Claim 1, wherein said acid is sulphurous acid H2SO3.
10. A method as defined in Claim 1, wherein said acid is hydrochloric acid HCl.
11. A method as defined in Claim 1, wherein said acid is nitric acid HNO3.
12. A method as defined in Claim 1, wherein said calcium containing salt is a soluble salt of calcium.
20~
20~
13. A method as defined in Claim 1, wherein said sulphate containing salt is a soluble salt of sulphate.
14. A method as defined in Claim 1, wherein said aluminium containing salt is a soluble salt of aluminium.
15. A method as defined in Claim 1, wherein the concentration of the calcium sulphate hemihydrate in the mixture is between 5% and 25%.
16. A method as defined in Claim 1, wherein said acid is from about 0.01% to 5%
weight percent of the final mixture.
weight percent of the final mixture.
17. A method as defined in Claim 1, wherein said calcium containing salt is from about 0.01% to 5% weight percent of the final mixture.
18. A method as defined in Claim 1, wherein said sulphate containing salt is from about 0.01% to 5% weight percent of the final mixture.
19. A method as defined in Claim 1, wherein said aluminium containing salt is from about 0.01% to 5% weight percent of the final mixture.
20. A method as defined in Claim 1 in which the needle shape calcium sulphate dihydrate crystals have a mean particle size of about 5-35 micrometers in length and about 1-5 micrometers in diameter.
21. A method for using needle shape calcium sulphate dihydrate as filler for papermaking, by adding the calcium sulphate dihydrate filler suspension produced according to Claim 1 directly to the papermaking furnish.
22. A method for using needle shape calcium sulphate dihydrate as filler for papermaking characterized by adding the calcium sulphate dihydrate filler produced according to Claim 1 after filtration in a dry form to the papermaking furnish.
23. Water insoluble finely divided calcium sulphate comprising a mixture of calcium sulphate suspension, a calcium-chelating agent, with or without a weak acid, at high temperature, where the calcium sulphate is coated by and is in equilibrium with the calcium-chelating agent and/or the weak acid the mixture.
24. Water insoluble finely divided calcium sulphate as defined in Claim 23 wherein said calcium sulphate is calcium sulphate anhydrate.
25. Water insoluble finely divided calcium sulphate as defined in Claim 23 wherein said calcium sulphate is calcium sulphate hemihydrate.
26. Water insoluble finely divided calcium sulphate as defined in Claim 23 wherein said calcium sulphate is ground calcium sulphate dihydrate.
27. Water insoluble finely divided calcium sulphate as defined in Claim 23 wherein said calcium sulphate is byproduct calcium sulphate dihydrate.
28. Water insoluble finely divided calcium sulphate as defined in Claim 23 wherein said calcium sulphate is precipitated calcium sulphate dihydrate.
29. Water insoluble finely divided calcium sulphate dihydrate as defined in Claim 23 wherein said weak acid is phosphoric acid H3PO4.
30. Water insoluble finely divided calcium sulphate dihydrate as defined in Claim 23 wherein said weak acid is metaphosphoric acid (HPO3)n.
31. Water insoluble finely divided calcium sulphate dihydrate as defined in Claim 23 wherein said weak acid is hexametaphosphoric acid (HPO3)6.
32. Water insoluble finely divided calcium sulphate dihydrate as defined in Claim 23 wherein said chelating agent is an alkali metal salt of a weak acid.
33. Water insoluble finely divided calcium sulphate dihydrate as defined in Claim 23 wherein said chelating agent is an alkali earth metal salt of a weak acid.
22~
22~
34. Water insoluble finely divided calcium sulphate dihydrate as defined in Claim 23 wherein said chelating agent is sodium hexametaphosphate.
35. Water insoluble finely divided calcium sulphate dihydrate as defined in Claim 23 wherein said calcium chelating agent is from about 0.001% to 10% weight percent of the final mixture.
36. Water insoluble finely divided calcium sulphate dihydrate as defined in Claim 23 wherein said weak acid is from about 0.001% to 10% weight percent of the final mixture.
37. Water insoluble finely divided calcium sulphate dihydrate as defined in Claim 23 wherein said high temperature means between 30°C and 90°C.
38. Water insoluble finely divided calcium sulphate dihydrate as defined in Claim 23 wherein said high temperature means heating the mixtures for 5 to 60 minutes.
39. A method of making water insoluble finely divided calcium sulphate dihydrate in a slurry comprising the successive steps of calcium sulphate dihydrate dispersion, chelating agent addition with or without a weak acid addition and agitation at high temperature.
40. A method as defined in Claim 39 wherein said slurry is a 5-25% weight percent calcium sulphate dihydrate aqueous slurry.
41. A method as defined in Claim 39 wherein said chelating agent addition is making a mixture of a calcium sulphate dihydrate slurry as defined in Claim 40 and a calcium-chelating agent.
42. A method as defined in Claim 39 wherein said weak acid addition is making a mixture of a calcium sulphate dihydrate slurry and a calcium-chelating agent or conjugate base defined in Claim 41 and a weak acid.
43. A method as defined in Claim 39 wherein said agitation of the final mixture is making a mixture of a calcium sulphate dihydrate slurry, a calcium-chelating agent or conjugate base and a weak acid defined in Claim 42 agitating the final mixture to ensure uniform mixing.
44. A method as defined in Claim 39 wherein said calcium sulphate is calcium sulphate anhydrate.
45. A method as defined in Claim 39 wherein said calcium sulphate is calcium sulphate hemihydrate.
46. A method as defined in Claim 39 wherein said calcium sulphate is ground calcium sulphate dihydrate.
47. A method as defined in Claim 39 wherein said calcium sulphate is byproduct calcium sulphate dihydrate.
48. A method as defined in Claim 39 wherein said calcium sulphate is precipitated calcium sulphate dihydrate.
49. A method as defined in Claim 39 wherein said weak acid is phosphoric acid H3PO4.
50. A method as defined in Claim 39 wherein said weak acid is metaphosphoric acid (HPO3)n.
51. A method as defined in Claim 39 wherein said weak acid is hexametaphosphoric acid (HPO3)6.
52. A method as defined in Claim 39 wherein said chelating agent is an alkali metal salt of a weak acid.
53. A method as defined in Claim 39 wherein said chelating agent is an alkali earth metal salt of a weak acid.
54. A method as defined in Claim 39 wherein said chelating agent is sodium hexametaphosphate.
55. A method as defined in Claim 39 wherein said calcium chelating agent is from about 0.001% to 10% weight percent of the final mixture.
56. A method as defined in Claim 39 wherein said weak acid is from about 0.001% to 10% weight percent of the final mixture.
57. A method as defined in Claim 39 wherein said agitation of the final mixture is from 1 to 15 minutes.
58. A method as defined in Claim 39 wherein said warming up means heating the mixtures between 30°C and 90°C.
59. A method as defined in Claim 39 wherein said warming up means heating the mixtures between 5 and 60 minutes.
60. A method for using water insoluble needle shape calcium sulphate dihydrate as filler for papermaking characterized by adding the calcium sulphate dihydrate filler suspension produced according to Claim 39 directly to the papermaking furnish.
61. A method for using water insoluble needle shape calcium sulphate dihydrate as filler for papermaking characterized by adding the calcium sulphate dihydrate filler produced according to Claim 39 after filtration in a dry form to the papermaking furnish.
Priority Applications (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2355027 CA2355027A1 (en) | 2001-08-13 | 2001-08-13 | Process for the production of water insoluble needle-shaped precipitated calcium sulphate dihydrate (caso4-2h2o) and its use as a filler in papermaking |
| CA002367593A CA2367593C (en) | 2001-08-13 | 2002-01-15 | Method of reducing the solubility of calcium sulfate dihydrate in an aqueous suspension and method of making the same |
| US10/486,762 US20040241082A1 (en) | 2001-08-13 | 2002-08-09 | Method of reducing the solubility of calcium sulfate dihydrate in an aqueous suspension and method of making same |
| PCT/CA2002/001244 WO2003016216A2 (en) | 2001-08-13 | 2002-08-09 | Method of reducing the solubility of calcium sulfate dihydrate in an aqueous suspension and method of making the same |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2355027 CA2355027A1 (en) | 2001-08-13 | 2001-08-13 | Process for the production of water insoluble needle-shaped precipitated calcium sulphate dihydrate (caso4-2h2o) and its use as a filler in papermaking |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2355027A1 true CA2355027A1 (en) | 2003-02-13 |
Family
ID=4169724
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2355027 Abandoned CA2355027A1 (en) | 2001-08-13 | 2001-08-13 | Process for the production of water insoluble needle-shaped precipitated calcium sulphate dihydrate (caso4-2h2o) and its use as a filler in papermaking |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2355027A1 (en) |
-
2001
- 2001-08-13 CA CA 2355027 patent/CA2355027A1/en not_active Abandoned
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued | ||
| FZDE | Discontinued |
Effective date: 20031114 |