Abstract: Methods are provided for producing a composition comprising carbonates, wherein the methods comprise utilizing waste sources of metal oxides. An aqueous solution of divalent cations, some or all of which are derived from a waste source of metal oxides, may be contacted with CO2 and subjected to precipitation conditions to provide compositions comprising carbonates. In some embodiments, a combustion ash is the waste source of metal oxides for the aqueous solution containing divalent cations. In some embodiments, a combustion ash is used to provide a source of proton-removing agents, divalent cations, silica, metal oxides, or other desired constituents or a combination thereof.

Abstract: Both a process and an apparatus whereby a fuel with both a high carbon content, a relatively high sulphur content and a relatively low ash content, can be combusted without the release of potentially damaged amounts of carbon dioxide and sulphur dioxide are described. Further, the process and apparatus each provide an operation whereby the carbon dioxide and sulphur dioxide emissions form the combustion of a carbonaceous fuel with both a high carbon content and a relatively high sulphur content can each be recovered as a useable product. Typically the fuel is petroleum coke, or certain grades of anthracite, coal and natural gas.

Abstract: A method for effectively absorbing and removing CO2 in an exhaust gas generated during an industrial process for reducing the amount of CO2 that is exhausted into the atmosphere. The exhaust gas containing CO2 is blown into an agglomerate of solid particles containing CaO and/or Ca(OH)2 so that the CO2 is in contact with the agglomerate for fixing the CO2 in the exhaust gas as CaCO3, thereby reducing the CO2 concentration in the exhaust gas. Preferably, the solid particles contain water, and more preferably, the solid particles contain surface adhesive water.

Abstract: Method for producing nanosized calcium hydroxide crystals or particles, according to which method the calcium oxide-bearing initial material is brought into contact with carbon dioxide in the aqueous phase. Calcium carbonate crystals or particles are produced in a mixture, the pH of which is below 7. Using the present invention, it is possible to combine the two stages of producing CaCO3 particles into one entity, in which case the overall processing time is shortened and the use of external energy is minimized.

Abstract: Process for the production of precipitated calcium carbonate particles, structured at the nanoscale, by carbonation of milk of lime in the presence of a crystallization controller selected from the following list: polyaspartic acid, dioctyl sodium sulphosuccinate, polyacrylic acid, the molecular weight of which is between 500 and 15 000, and citric acid. When the crystallization controller is citric acid, its concentration in the milk of lime is between 5 and 15%.

Abstract: The invention relates to a method for producing a sheet of paper (6) comprising paper fibres and calcium carbonate mainly in the form of calcite crystals linked directly to the paper fibres. The inventive method is characterised in that it comprises the following steps:—(i) an aqueous composition comprising calcium bicarbonates (5) and/or hydrated and/or dissolved carbon dioxide (3) and (ii) an aqueous composition comprising calcium hydroxide (4) are mixed in an aqueous medium in such a way as to precipitate the calcium carbonate in the form of vaterite crystals;—paper fibres (2, 2?) are immediately added;—the vaterite crystals are left to transform into calcite crystals on contact with the fibres;—said mixture containing the calcite crystals which are fixed to the fibres is subsequently sent on the conveying wire of the papermaking machine (M) for drainage and so that the sheet of paper can be formed;—the sheet of paper (6) thus obtained is treated, if necessary, and dried.

Abstract: Process for the production of precipitated calcium carbonate particles, structured at the nanoscale, by carbonation of milk of lime in the presence of a crystallization controller selected from the following list: polyaspartic acid, dioctyl sodium sulphosuccinate, polyacrylic acid, the molecular weight of which is between 500 and 15 000, and citric acid. When the crystallization controller is citric acid, its concentration in the milk of lime is between 5 and 15%.

Abstract: The present invention provides a method for making precipitated calcium carbonate (PCC) which compensates for the slow reaction time of carbonation in a manner which reduces or eliminates the undesirable use and expense of added equipment and processes of previously known methods. The method of the invention involves the generation of multiple streams (preferably at least twenty-five streams) of carbon dioxide which are co-currently introduced to a flow of calcium hydroxide slurry (lime milk). By use of multiple gas streams an intimate mixing of carbon dioxide with the slurry is achieved which compensates for the slow reaction time of carbonation while reducing or eliminating the need for equipment and processes related to recycling, batch operation, serial operation, and long reactor length. An additional benefit of using multiple gas streams in co-current flow is a lower concentration gradient of PCC formed therein facilitating the formation of smaller particles.

Abstract: Process for making a solid compound by precipitation, using a high intensity mixing reactor and comprising the steps of (A) introducing a first fluid material containing a first reactant and a second fluid material containing a second reactant into said reactor, in order to obtain a mixed fluid, in order to cause the first reactant to react with the second reactant to form a solid compound by precipitation in the mixed fluid; (B) withdrawing the mixed fluid containing the precipitated solid obtained in step (A) from the reactor, and; (C) optionally separating the precipitated solid compound from at least one fraction of the mixed fluid.

Abstract: Novel and innovative PCC pigments, having a reduced production cost, able to be used in a paper coating formulations to manufacture coated high-quality matt papers, in particular for inkjet applications. Process for the preparation of same, using a reduced flow rate of a carbon dioxide-containing gas in the PCC carbonation step, which produces stable, porous, agglomerates of PCC featuring unique properties and structure, this step being followed by an upconcentration step to increase the solids content.

Abstract: To provide a process for producing carbonate particles, capable of efficient, easy formation of carbonate particles which have high crystallinity, less prone to agglomeration and offer orientation birefringence, particularly carbonate particles that are needle- or rod-shaped, and of controlling the particle size. In the process a metal ion source and a carbonate ion source are heated together in a liquid of 55° C. or higher for reaction to produce carbonate particles with an aspect ratio of greater than 1, wherein the metal ion source contains at least one metal ion selected from the group consisting of Sr2+, Ca2+, Ba2+, Zn2+ and Pb2+. The carbonate particles are preferably needle- or rod-shaped, pH of the liquid after heating reaction is preferably 8.20 or more, and in its X-ray diffraction spectrum the full-width at half maximum of the diffraction peak corresponding to (111) plane is preferably less than 0.8°.

Abstract: To provide a method for producing a carbonate, including: growing seed crystals, wherein the seed crystals are grown in a reaction solution containing at least urea. An aspect in which the seed crystals are strontium carbonate particles, an aspect in which the reaction solution contains a metal ion source and the metal ion source is a hydroxide of strontium, and the like are favorable.

Abstract: The present invention provides a method for producing carbonates, which includes at least adding an aqueous solution containing a carbonate source into an alcoholic solution containing a metal ion source, wherein an alkaline chemical is added when the carbonate source is reacted with the metal ion source.

Abstract: A method and apparatus for improving contact between a liquid and a reactant gas by moving the liquid in a serpentine path that moves horizontally and vertically through individual chambers or stations in an elongated tank or reactor and introducing a reactant gas into the liquid in one or more of the stations or chambers as the liquid moves through the tank or reactor.

Abstract: Methods of obtaining a solution of calcium ions from lime (e.g. carbide lime) are disclosed. In one aspect the method comprises (i) treating the lime with an aqueous solution of a polyhydroxy compound (preferably sorbitol) having three or more hydroxy groups and a straight chain of 3 to 8 carbon atoms; and (ii) optionally separating insoluble impurities from the solution resulting from (i). In another aspect the method comprises (iii) treating carbide lime with an aqueous solution of a polyhydroxy compound (e.g. sorbitol or sucrose) to extract calcium from the carbide lime; and (iv) separating insoluble impurities from the solution resulting from (i). The solutions obtained may be treated with precipitating agent to obtain a solid calcium containing product. The product may be calcium carbonate obtained by treating the solution with carbon dioxide as the precipitating agent.

Abstract: Calcium carbonate with high brightness is prepared by treating calcium carbonate and/or the milk of lime used for its preparation by reacting milk of lime with carbon dioxide and/or at least one of the calcium-containing preliminary products used for the preparation of the milk of lime before, during and/or after this reaction with a bleaching agent which comprises at least one compound of the formula (I): A[(CR1R2)SOpM(1/q)]r??(I) where the variables have the following meanings: A is NR3R4, NR3, N or OH; R1, R2, R3, R4 independently of one another, are hydrogen or an organic radical; M is ammonium or metal p is 2 or 3; q is the valency of M; and r is 1 when A = OH or NR3R4, is 2 when A = NR3 and is 3 when A = N; and where variables, if a mixture of compounds is used and/or r=2 or 3, are chosen independently of one another for each individual compound and/or for each [(CR1R2)SOpM(1/q)] group.

Abstract: A method for forming calcium carbonate is provided, the method comprising the steps of: (a) milling calcium hydroxide; (b) providing a reactor vessel containing a slurry of the milled calcium hydroxide; and (c) carbonating the slurry of the milled calcium hydroxide by introducing carbon dioxide into the reactor vessel to form basic calcium carbonate by a precipitation reaction, wherein the initial reaction temperature is from about 8° C. to about 15° C.

Abstract: A thermal ink jet recording paper, incorporating dewatered and milled precipitated calcium carbonate (“PCC”) is disclosed. Precipitated calcium carbonate is dewatered and milled in the presence of an amphoteric or anionic dispersant to produce a high solids PCC composition. When used in coating formulations the PCC has a surface morphology and chemistry that enhances the printability of ink jet paper. Ink jet recording paper incorporating the PCC of the present invention has reduced ink feathering and spreading as well as improved optical density, dry time, and water fastness.

Abstract: Feeding device for feeding burned lime to a reaction vessel for causticizing a soda liquor to caustic soda. The feeding device, in its upper part, comprises an inlet for a slurry of the burned lime and the soda liquor for formation of said slurry inside said feeding device. The system further comprises a tall and slender feed vessel having a lower part having an outlet defined therein for the slurry. The outlet, via a pump, is operatively connected to the reaction vessel. The process and the feeding system utilize the feeding device, in which process the slurry is created of the burned lime and a first part of the soda liquor, a second part being preheated before addition to the slurry, whereafter slaking and causticizing reactions are completed under elevated temperature and pressure.

Abstract: A process for the preparation of platy precipitated calcium carbonate comprising the steps of providing a suspension of calcium hydroxide, carbonating the suspension of calcium hydroxide, adding a polyacrylate to the suspension prior to the completion of carbonation to precipitate platy calcium carbonate. Also provided are a paper that is filled and a paper that is coated using the platy precipitated calcium carbonate according to the present invention.

Abstract: A process for the preparation of platy PCC comprising the steps of providing a suspension of calcium hydroxide, carbonating the suspension of calcium hydroxide, adding a condensed phosphate to the suspension prior to the completion of carbonation to precipitate platy calcium carbonate. A paper that is filled is also provided and a paper that is coated and a polymer that is filled are envisioned that use the platy PCC according to the present invention.

Abstract: Calcium carbonate in the form of aragonite crystals suitable for use as a filler for papermaking to give useful properties for bulk, whiteness, opacity, wire abrasion and yield is obtained by taking advantage of the causticization step. Herein disclosed is a process for producing calcium carbonate in the form of aragonite crystals which is useful as a filler for papermaking via the causticization step of the sulfate or soda pulping process, comprising adding an aqueous alkaline solution having a hydroxide ion level of 3 mol/l or less and containing 0.25 mol or less of carbonate ion per 1 mol of quick lime to quick lime and/or slaked lime at a quick lime concentration of 1–60% by weight with stirring to prepare milk of lime, and then adding green liquor to said milk of liquor at a loading rate of 0.002–0.12 g (sodium carbonate)/min/g (quick lime) to perform a causticization reaction at a temperature of 30–105° C.

Abstract: Silica-calcium carbonate composition particles having the characteristics of both synthetic silica and calcium carbonate are described along with paper having the particles internally filled therein and a method for making the particles. In the carbonation reaction, which typically involves a step of forming calcium carbonate, while agitating a calcium hydroxide slurry, a mixed gas of carbon dioxide and air is introduced thereinto and synthetic silica, such as colloidal silica or the like, is added before the carbonation rate arrives at 95% but after commencement of the carbonation reaction, followed by further introduction of the mixed gas to continue the carbonation reaction and completion of the carbonation reaction at the time when the pH of the slurry reaches 7, thereby providing the composite particles.

Abstract: A method and apparatus for the production of calcium carbonate and calcium silicate in common superatmospheric reactors. Multiple reactors can be provided for switching production between reactors, and advantageously utilizing process waste heat. On site production of both PCC and Calcium Silicate Hydrates is thus achieved in a paper mill.

Abstract: A process for producing hydrogen gas from a reaction of an organic substance and a base with a recycling of a carbonate or bicarbonate by-product and a regeneration of the base. In one embodiment, reaction of an organic substance and a base produces hydrogen gas and a metal carbonate. The instant invention provides recycling of the metal carbonate by-product. In a preferred embodiment, the metal carbonate by-product is soluble and recycling includes a three step process. In a first step, the soluble metal carbonate is reacted with a metal hydroxide to form a weakly soluble or insoluble metal carbonate that precipitates in a metathesis reaction. The metal hydroxide reactant of the hydrogen producing reaction is also formed in the metathesis reaction and remains in solution. Precipitation of the carbonate thus permits ready isolation of the carbonate by-product, while leaving behind an aqueous metal hydroxide phase that can be returned to and further utilized in the hydrogen producing reaction.

Abstract: Titanium dioxide-calcium carbonate composite particles capable of realizing characteristic properties inherent in titanium dioxide such as a high opacity, a process for producing the same, and a complex composition or complex incorporated with the same are provided. The composite particles were prepared by adding titanium dioxide particles having an average particle diameter of 0.1 to 0.5 ?m in a carbonation step, typically a step of introducing a gaseous mixture of carbon dioxide and air into a calcium hydroxide slurry with stirring, to conduct a carbonation, and continuing the reaction till pH of the slurry becomes 7 by continuous introduction of the gaseous mixture. Moreover, by incorporating the formed composite particles, complexes such as coatings and paints for paper making or composite materials such as paper, plastic molded materials, and rubber molded materials are produced.

Abstract: An abrasive precipitated calcium carbonate is provided that provides excellent cleaning properties without being excessively abrasive or damaging to gums or tooth surfaces. The abrasive, precipitated calcium carbonate has a primary particle size of about 1 ?m to about 4 ?m, and an aggregate size of about 3 ?m to about 10 ?m. Also disclosed is a method for forming calcium carbonate comprising the steps of: providing a reaction medium; introducing carbon dioxide and the calcium hydroxide slurry simultaneously into a reaction medium to form calcium carbonate while maintaining constant pH during calcium carbonate precipitation; and optionally drying the calcium carbonate slurry to form a dried calcium carbonate product. Also disclosed is a dentifrice containing the aforementioned abrasive, precipitated calcium, and one or more ingredients selected from the group consisting of humectants, thickening agents, binders, gums, stabilizing agents, antibacterial agents, fluorides, sweeteners, and surfactants.

Abstract: A process for the preparation of platy precipitated calcium carbonate comprising the steps of providing a suspension of calcium hydroxide, carbonating the suspension of calcium hydroxide, adding a polyacrylate to the suspension prior to the completion of carbonation to precipitate platy calcium carbonate. Also provided are a paper that is filled and a paper that is coated using the platy precipitated calcium carbonate according to the present invention.

Abstract: A process for the preparation of platy PCC comprising the steps of providing a suspension of calcium hydroxide, carbonating the suspension of calcium hydroxide, adding a condensed phosphate to the suspension prior to the completion of carbonation to precipitate platy calcium carbonate. A paper that is filled is also provided and a paper that is coated and a polymer that is filled are envisioned that use the platy PCC according to the present invention.

Abstract: This invention relates to calcium carbonate of different shapes including spindle, petal, whisker, needle, flake, ball and fiber. The calcium carbonate of such different shapes has an average particle size in the range of 10 nm-2.5 &mgr;m. This invention also relates to a process for preparing the said calcium carbonate with a controllable range of average particle size and different shapes. Precipitated powder of calcium carbonate with a desired shape and a controllable average particle size is obtained by carbonizing a suspension of calcium hydroxide and a feed gas containing carbon dioxide on a revolving bed under the gravitational field, and optionally in the presence of a crystal form-controller and/or crystal seeds. The precipitated powder of calcium carbonate obtained by the process according to this invention has a controllable average particle size and a narrow particle distribution.

Abstract: The present invention provides a low-cost carbon dioxide fixation method that allows effective usage of a large amount of generated coal ashes, and effective fixation of carbon dioxide included in flue gas generated from coal, refuse, or waste product, as well as improvement in the applicability of coal ashes to various applications and effective usage of by-product carbonate. Carbon dioxide is absorbed and fixated by subjecting the flue gas to gas-liquid contact with coal ash water slurry or coal ash eluate so as to make the carbon dioxide in the flue gas react and be absorbed thereinto, thereby fixating the carbon dioxide as carbonate. This method can be favorably used for disposal of flue gas from a boiler at a coal thermal power plant.

Abstract: A method for making a white synthetic carbide lime filler composition of calcium hydroxide and calcium carbonate, wherein the calcium carbonate is in the form of surface carbonation on the calcium hydroxide. The method can include calcining calcium carbonate, hydrating the calcined material under controlled conditions which maintain a low moisture content and fracture the hydrated material into small particles of calcium hydroxide, carbonating the small calcium hydroxide particles to create the surface carbonation of calcium carbonate, and classifying the carbonated synthetic carbide lime particles to separate off oversized particles. The method can use a combined classifying and carbonating process, and a modified classifying vessel can be provided to carry out the combined process.

Abstract: A dentrifice comprising granules consisting essentially of calcium carbonate particles, the granules having an average size of 50 to 500 um and a crushing resistance of 1 to 20 g/granule, and the calcium carbonate particles having a primary particle size of 0.01 to 0.5 um.

Abstract: An environmentally friendly process for the production of precipitated calcium carbonate suitable for industrial application from a calcium carbonate-rich by-product of a nitrophosphate fertilizer plant. The process employs purification steps of calcination, carbonation and optional treatment with an emulsion of fatty acid or fatty acid derivatives.

Abstract: Process for the production of precipitated calcium carbonate particles, structured at the nanoscale, by carbonation of milk of lime in the presence of a crystallization controller selected from the following list: polyaspartic acid, dioctyl sodium sulphosuccinate, polyacrylic acid, the molecular weight of which is between 500 and 15 000, and citric acid. When the crystallization controller is citric acid, its concentration in the milk of lime is between 5 and 15%.

Abstract: According to the process, limestone is burned at a high temperature to form calcium oxide and, thereafter, calcium carbonate is formed from calcium oxide in the presence of water and carbonate ions and the formed calcium carbonate is recovered. The formation of the carbonate may be performed by carbonating calcium oxide with carbon dioxide gas in the presence of water or water vapour, or by reacting calcium oxide with soda solution. According to the invention calcium oxide is converted to calcium carbonate without separate slaking and essentially without intermediate storage, in particular without intermediate storage between the burning of the starting material and the forming of calcium carbonate. With the aid of the invention a quite advantageous solution in view of heat economy is achieved.

Abstract: The present invention concerns a process for preparing calcium carbonate pigment from calcium oxide and/or calcium hydroxide and carbon dioxide in the presence of water. According to the invention, the starting materials are reacted in fluid state containing at least 20 parts of volume of gas for each part by volume of suspension formed by water and solid substances, and the amount of water is essentially equivalent to the amount which is evaporated during the reaction together with the amount left in a calcium carbonate product which behaves like a powder. By means of the present invention, PCC in powder form can be prepared without the product first having to be separated from a slurry.

Abstract: Disclosed is a novel form of particulate precipitated aragonite calcium carbonate and a novel process for producing it.

Abstract: The present invention provides a method of reducing the detrimental environmental impact of an industrial plant which produced or produces a product selected from the group consisting of calcium oxide, also known as lime, and carbon dioxide gas, the method comprising the step of forming an environmentally less detrimental composition from such product which composition comprises predominantly calcium carbonate.

Abstract: Disclosed is a novel form of particulate precipitated aragonite, and a novel process for producing it.

Abstract: Inexpensive spindle- or rice-like calcium carbonate giving useful properties for brightness, opacity and wire abrasion resistance as a paper filler is provided by taking advantage of the causticization step. When a white liquor is used for slaking a quick lime, the quick lime used in the slaking reaction of a first step has a calcium carbonate content of 10% by weight or less and is slaked with the white liquor at a concentration of 20 to 60% to prepare a milk of lime. When a green liquor is used for slaking a quick lime, the quick lime used in the slaking reaction of a first step has a calcium carbonate content of 0.1 to 10% by weight and is slaked with the green liquor at a concentration of 20 to 60% to prepare a milk of lime. In a second step, causticization reaction takes place at a green liquor loading rate of 0.02 to 0.5 cc (green liquor)/min/g (quick lime) at a reaction temperature of 20 to 105° C. to afford spindle- or rice-like calcium carbonate.

Abstract: A method of making a composite pigment of precipitated calcium carbonate (PCC) and a silicon compound, in which the resulting composite pigment is endowed with an excellent combination of optical and mechanical properties. Among other things, a PCC/silicate composite pigment made according to this invention imparts increased bulk, light scattering power, porosity and printing properties to paper. The composite pigment material made according to this invention also is very competitive from the standpoint of its production cost. The method for making the composite pigment includes the step of introducing a soluble silicate compound into an aqueous medium containing a precipitate of calcium carbonate formed by carbonation of lime milk, and at a time when the calcium carbonate precipitation reaction has progressed to near completion.

Abstract: A pigment product suitable for use in a coating composition to provide a gloss coating on paper, the pigment product comprising a processed particulate kaolin whose particles have a particle size distribution such that at least 80% by weight of the particles have an equivalent spherical diameter less than 2 &mgr;m and not less than 8%, preferably not less than 12%, by weight of the particles have an equivalent spherical diameter less than 0.25 &mgr;m and whose particles have a shape factor of at least 45, preferably at least 50.

Abstract: A method of continuously or semi-continuously producing a solid product comprising precipitated calcium carbonate in an aqueous medium which method comprises delivering an aqueous suspension of calcium hydroxide in sequence through a series of at least two static in-line mixers whilst carbon dioxide is introduced into the suspension at or before each of the mixers whereby carbon dioxide and the aqueous suspension are intimately mixed in each mixer to facilitate reaction of the carbon dioxide with calcium hydroxide dissolved in the aqueous medium, the calcium hydroxide in the suspension delivered to the series of static in-line mixers being progressively consumed and converted to calcium carbonate as the suspension passes through the series.

Abstract: The invention concerns precipitated calcium carbonate products containing polynuclear regular agglomerates having a number of calcium carbonate particles (aggregates) attached to each other and having a particle size of about 40 to 200 nm. According to the invention, these products are prepared by adjusting the Z potential of the calcium carbonate suspension to −1 . . . −20 mV by adjusting the pH of the suspension to 6.5 . . . 9.5. The pH of the calcium carbonate slurry obtained by causticizing is adjusted to a desired value in a box filter, where after the suspension is stirred by a heavy-duty mixer such that it is subjected to differences of about 50 to 200 m/s in peripheral speed. The products according to the invention have good opacity and are very well suited for coating paper.

Abstract: An environmental friendly process for the production of finely divided calcium carbonate suitable for industrial application from calcium carbonate rich by-product of nitrophosphate fertiliser plant by adopting purification steps of thermal treatment, pulverization and coating using emulsion of fatty acid or its derivatives.

Abstract: An environmental friendly process for the production of precipitated calcium carbonate suitable for industrial application from calcium carbonate rich by-product of nitrophosphate fertilizer plant by adopting purification steps of calcination, carbonation and optional treatment with emulsion of fatty acid or its derivatives.

Abstract: Inexpensive spindle- or rice-like calcium carbonate giving useful properties for brightness, opacity and wire abrasion resistance as a paper filler is provided by taking advantage of the causticization step. When a white liquor is used for slaking a quick lime, the quick lime used in the slaking reaction of a first step has a calcium carbonate content of 10% by weight or less and is slaked with the white liquor at a concentration of 20 to 60% to prepare a milk of lime. When a green liquor is used for slaking a quick lime, the quick lime used in the slaking reaction of a first step has a calcium carbonate content of 0.1 to 10% by weight and is slaked with the green liquor at a concentration of 20 to 60% to prepare a milk of lime. In a second step, causticization reaction takes place at a green liquor loading rate of 0.02 to 0.5 cc (green liquor)/min/g (quick lime) at a reaction temperature of 20 to 105° C. to afford spindle- or rice-like calcium carbonate.

Abstract: A pigment product suitable for use in a coating composition to provide a gloss coating on paper, the pigment product comprising a processed particulate kaolin produced from a naturally platy kaolin clay having a particle size distribution such that about 50% to 60% by weight of the particles have an esd less than 2 &mgr;m and less than 25% by weight of the particles have an esd less than 0.25 &mgr;m and a shape factor of at least 15. This platy clay can be blended with b-fraction clay component. In processing, the crude kaolin is ground to a shape factor greater than 50 to produce even greater “platy” clay. The pigment product has a particle size distribution such that at least 80% by weight of the particles have an esd less than 2 &mgr;m and greater than 12% and less than 35% by weight of the particles have an esd less than 0.25 &mgr;m and whose surface area is greater than 12 m2/g when measured by the BET method.

Abstract: There is disclosed a method for the preparation of a precipitated calcium carbonate (PCC) for use as a pigment in paper coating compositions, the method comprising the steps of (a) carbonating an aqueous lime-containing medium to produce an aqueous suspension of a PCC predominantly in a selected crystal form, (b) at least partially dewatering the PCC-containing suspension; and (c) subjecting the PCC-containing suspension to comminution by high shear attrition grinding with an attrition grinding medium. Steps (b) and (c) may be applied in either order, ie. (b) followed by (c) or alternatively (c) followed by (b). The dewatering step (b) is preferably carried out using a pressure filter device operating at a pressure of at least 5 MPa, preferably at least 10 MPa. A pH reduction step may be applied after steps (b) and (c). Also disclosed are pigments produced by the method and pigment and paper coating compositions including such pigments.