WO2008154614A1

WO2008154614A1 - Methods for dewatering kaolin clay slurries and kaolin-clay filter cakes and kaolin-clay slurries made therefrom

Info

Publication number: WO2008154614A1
Application number: PCT/US2008/066650
Authority: WO
Inventors: Ismail Yildirm; Robert J. Pruett
Original assignee: Imerys Pigments, Inc.
Priority date: 2007-06-13
Filing date: 2008-06-12
Publication date: 2008-12-18

Abstract

A method for dewatering a kaolin clay is provided. A flocculated kaolin clay slurry may be filtered using a membrane filter press to remove water, thereby leaving a filter cake. The filter cake may be optionally re-dispersed and/or dried. A kaolin-clay filter cake having at least 60% solids is also provided.

Description

METHODS FOR DEWATERING KAOLIN CLAY SLURRIES AND KAOLIN-CLAY FILTER CAKES AND KAOLIN-CLAY SLURRIES MADE THEREFROM

DESCRIPTION

This application claims priority to U.S. Provisional Patent Application No. 60/943,568, filed June 13, 2007, the contents of which are incorporated herein by reference.

Technical Field

[001] Disclosed herein are kaolin-clay filter cakes and methods for dewatering finely disseminated particulate materials, such as a kaolin clay slurry.

Background

[002] Kaolin is a white inorganic pigment obtained from kaolin clay. Large deposits of kaolin clay exist in Devon and Cornwall, England and in Georgia and South Carolina, United States of America. Important deposits also occur in Brazil, Australia, and in several other countries. Kaolin clay, also referred to as china clay or hydrous kaolin, comprises predominantly mineral kaolinite (AI₂Si₂O₅(OH)₄), anhydrous aluminum silicate, and small amounts of various impurities.

[003] Kaolinite generally exists in the form of hydrous aluminosilicate crystals in the shape of thin hexagonal plates or booklets of platelets called "stacks". The individual plates may have mean diameters of 1 μm or less, but kaolinite particles in the form of stacks of plates may have an equivalent spherical diameter ("esd") of 10 μm or more. In general, kaolin clay particles having an esd of 2 μm or more are in the form of stacks of kaolinite plates, rather than individual plates.

[004] Transporting kaolin clays usually includes either transporting slurries comprising the kaolin clay to the end user or preparing dry or substantially dry particulates from slurries comprising the kaolin clay. Current practices are thermally inefficient due to low amount of solids in the slurries fed to drying apparatus. Thus, a need exists for preparing higher solids filter cakes and slurries prepared from those filter cakes, thereby decreasing energy costs due to smaller drying requirements.

SUMMARY

[005] Disclosed herein are methods for dewatering nanodimensional particulate materials, for example, kaolin clays. In one embodiment, the method comprises providing a fine kaolin slurry having a particle size distribution such that at least about 70% by weight of the kaolin particles have a particle size less than about 0.5 microns and a solids content of less than about 55%, and filtering said flocculated kaolin slurry in a membrane pressure filter to produce a filter cake having a solids content of at least about 60%. In one embodiment, the particle size distribution of the kaolin slurry is up to 98% by weight less than 0.5 microns. In yet another embodiment, the particle size distribution of the kaolin slurry is at least about 85% by weight less than 2 microns. In another embodiment, the filter cake may be re-dispersed, forming a high solids slurry. In a further embodiment, the fine kaolin slurry may be further processed by at least one of drying, milling, and calcining. In yet another embodiment, the filter cake may undergo drying, milling, and/or calcining. In yet a further embodiment, the fine kaolin slurry may undergo at least one of a beneficiation step, flocculating, degritting, classification, and other refining steps before undergoing the filtering step.

[006] Also disclosed herein are kaolin-clay filter cakes. In one embodiment, a kaolin-clay filter cake comprising at least about 60% clay solids is disclosed. In another embodiment, the kaolin-clay filter cake comprises at least about 62% solids. In a further embodiment, the kaolin-clay filter cake comprises at least about 64% solids. In yet another embodiment, the kaolin-clay filter cake comprises at least about 68% solids.

[007] Additional advantages will be set forth in part in the following description, and in part will be obvious from the description, or may be learned by practice of the invention. Advantages will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. [008] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.

DESCRIPTION OF THE EMBODIMENTS

[009] Disclosed herein are methods for dewatering nanodimensional particulate materials. As used herein, a nanodimensional particulate material is one having at least one dimension less than 1 μm. In one embodiment, the nanodimensional particulate material is kaolin clay. In another embodiment, the nanodimensional particulate material is calcium carbonate In yet another embodiment, the nanodimensional particulate material is precipitated calcium carbonate. The skilled artisan readily understands that the embodiments disclosed herein may utilize any nanodimensional particulate material, but for illustrative purposes, the material is described as a kaolin clay. The nanodimensional kaolin clay may be referred to as a nanokaolin. Nanokaolin comprises a particle size distribution such that about 70% to about 75% by weight of the kaolin is less than about 0.25 micron. In one embodiment, the d₅₀ of a nanokaolin is about 0.1 micron. In yet another embodiment, the d₅₀ of a nanokaolin is about 0.12 micron. As used herein, the term "d₅₀" refers to the median particle size, or the particle size value less than about which there are 50% by weight of the particles.

[010] In one embodiment, methods for dewatering fine kaolin clay slurries and kaolin-clay filter cakes having increased solids content are disclosed. A membrane filter press may be utilized to remove at least a portion of the water from the fine kaolin clay slurries. In one embodiment, the method comprises filtering at least one fine kaolin clay slurry using at least one membrane filter press, and producing at least one kaolin-clay filter cake having a solids content of at least about 60%. In another embodiment, the method may comprise any one or more of those steps and/or parameters disclosed in the Great Britain Patent Application filed on June 13, 2007, entitled "Dewatering Kaolin," which is incorporated by reference herein in its entirety.

[011] As used herein, fine kaolin clays refer to kaolin clays having a particle size distribution ("psd") such that at least about 70% of the clays have a psd less than about 0.5 μm. As will be appreciated by those skilled in the art, the psd of a particulate product may be determined by measuring the sedimentation speeds of the dispersed particles of the particulate product through a standard dilute aqueous suspension using a SEDIGRAPH instrument, e.g., SEDIGRAPH 5100 (Micromeritics Instrument Corporation; Norcross, GA, USA). The size of a given particle is expressed in terms of the diameter of a sphere of equivalent diameter that sediments through the suspension, that is, an equivalent spherical diameter or esd. The SEDIGRAPH instrument records the percentage by weight of particles having an esd less than a particular esd value, versus that esd value.

[012] The kaolin slurry may comprise at least two kaolin clay slurries, each slurry having a different particle size distribution. In one embodiment, at least one micron-sized kaolin clay slurry may be combined with at least one nanokaolin slurry.

[013] The kaolin slurry may be provided by any method now known or hereafter discovered. In one embodiment, the kaolin slurry is provided by blunging at least one kaolin clay chosen from at least one of crude kaolin clay and processed kaolin clay with water to form an aqueous suspension. The suspension can be a blended kaolin suspension, comprising a combination of crude and processed kaolin clays. Blunging the kaolin clay disseminates the clay particles. In one embodiment, blunging comprises mixing the kaolin clay with at least one dispersing agent. Exemplary dispersing agents include, but are not limited to, sodium polyacrylate, ammonium polyacrylate, sodium hexametaphosphate, tetrasodium pyrophosphate, and sodium silicate. In another embodiment, blunging comprises mixing the kaolin clay with at least one pH regulator. Exemplary pH regulators include, but are not limited to, sodium hydroxide and ammonium hydroxide. In a further embodiment, blunging comprises mixing the kaolin clay with at least one dispersing agent and at least one pH regulator.

[014] The kaolin slurry may also undergo at least one degritting step to reduce the particle size of the kaolin slurry to less than about 45 μm. Degritting is directed to removing larger-size particles by passing the clay through separation equipment. Exemplary degritting equipment includes, but is not limited to, hydrocyclones, spiral classifiers, screen bowl centrifuges, and sieve screens having 325 mesh openings.

[015] The kaolin slurry may also undergo at least one classifying step to classify the clay into coarse and fine fractions by using any known or hereafter discovered method. Exemplary classifying methods include, but are not limited to: gravity sedimentation or elutriation; a hydrocyclone apparatus; a solid bowl decanter centrifuge; and a disc-nozzle centrifuge. The coarse fraction may be discarded, used as a separate product, and/or directed to a blend tank as an auxiliary source of coarse kaolin. Classification may separate the kaolin slurry such that from about 70% to about 98% of the particles have an esd of less than about 0.5 μm. Classifying the kaolin clays using, for example, disc-nozzle centrifuges, may also assist in partially, substantially, or fully removing at least one impurity from the kaolin slurry. Impurities that may be partially, substantially, or fully removed include, but are not limited to, anatase, iron oxides, silica, and mica. Nanodimensional kaolin clays may be prepared using at least one of disc-nozzle centrifuges and solid bowl decanter centrifuges.

[016] The kaolin slurry may be subjected to at least one grinding step now known or hereafter discovered. In one embodiment, the at least one grinding step comprises wet media grinding with at least one particulate grinding medium. In one embodiment, the particulate grinding medium is silica sand. In another embodiment, the particulate grinding medium has a relatively high specific gravity, for example, about 2 or more. In a further embodiment, the particulate grinding medium comprise grains of silica sand having diameters not larger than about 2 μm and not smaller than about 0.25 μm. The kaolin slurry may be separated from the at least one particulate grinding medium by any manner now known in the art or hereafter discovered. In one embodiment, the kaolin slurry is separated from the at least one particulate grinding medium by passing the slurry through a sieve of appropriate aperture size, for example, a sieve having nominal aperture sizes ranging from 0.1 mm to 0.25 mm.

[017] In another embodiment, the at least one grinding step is a comminution step in order to assisting in breaking down composite particles or aggregates of individual particles. Such composite particles generally comprise coherent stacks or blocks of individual hexagonal plate-like particles, and may be particularly present in the kaolin slurry when the kaolin clay is from a sedimentary deposit. In one embodiment, the comminution step comprises relatively gentle grinding with a wet particulate grinding medium. The term "relatively gentle grinding," as used herein, indicates grinding in an attrition-grinding mill with at least one particulate grinding medium, the contents of the attrition-grinding mill being agitated by an impeller rotating at a speed not sufficient to set up a vortex in the suspension, such as at a peripheral speed below 10 m/s, and in which the amount of energy dissipated in the suspension during grinding ranges up to about 200 kW- hr/ton. In one embodiment, the amount of energy dissipation ranges from about 0 to about 35 kW-hr/ton. In another embodiment, the amount of energy dissipation ranges from about 35 to about 200 kW-hr/ton. In a further embodiment, the amount of energy dissipation is equal to or less than about 75 kWh-hr/ton. In yet another embodiment, the amount of energy dissipation is equal to or less than about 55 kWh-hr/ton.

[018] In another embodiment, comminution at least partially breaks down many of the composite particles in the kaolin slurry into individual thin, substantially hexagonal plates (a process that may also be referred to as delamination), the result being an increase of the average shape factor of the kaolin clay in the slurry. In a further embodiment, comminition may increase the shape factor of the kaolin clay from a starting value of about 5 to about 10 to a shape factor of at least about 50. In yet another embodiment, comminution may increase the shape factor of the kaolin clay by about 40 or more.

[019] The kaolin slurry may be subjected to at least one conventional leaching (bleaching) agent now known or hereafter discovered. In one embodiment, the at least one leaching agent is a reductive leaching agent. Exemplary reductive leaching agents include, but are not limited to, sodium hydrosulfite and formamidine sulphinic acid. In another embodiment, the at least one leaching agent is added to the kaolin slurry in a dose range of about 0.5 to about 5 pounds per ton of kaolin clay. In a further embodiment, less than about 4 pounds of leaching agent per ton is added. In yet another embodiment, the kaolin slurry is subject to at least one conventional leaching agent at an acidic pH, for example, in the range of 2 to 4.

[020] The kaolin slurry may be subjected to at least one beneficiation step, either now known or hereafter discovered, to remove at least one impurity. In one embodiment, the at least one beneficiation step is a selective separation method now known in the art or hereafter discovered.

[021] In another embodiment, the at least one beneficiation step is a froth flotation treatment operation to remove titanium-containing impurities. In such an embodiment, the froth floatation treatment operation comprises conditioning the kaolin slurry with an oleic acid to coat the air bubbles produced in the float cells. The titanium-containing materials adhere to the air bubbles and are floated out of the kaolin slurry. One example of such a flotation process is described in U.S. Pat. No. 3,450,257 to Cundy. In one embodiment, the froth floatation treatment operation results in an improved brightness in the kaolin slurry, for example, a brightness gain ranging from about 0.1 to 3 GE units.

[022] In a further embodiment, the at least one beneficiation step comprises passing the kaolin clay through a high intensity magnetic separator to remove iron-containing impurities. In one embodiment, a standard high intensity wet magnetic separator is used. In another embodiment, the magnetic separation process results in an improved brightness in the kaolin slurry, for example, a brightness gain ranging from about 0.1 to 3 GE units.

[023] In yet another embodiment, the at least one beneficiation step is a flocculation process, in which impurities are flocced out of suspension while the kaolin slurry remains in suspension. In one embodiment, the at least one flocculating step occurs before the slurry is fed directly to a filter membrane press. In another embodiment, the slurry undergoes further processing steps before being fed to a filter membrane press. Any suitable flocculation polymer now known or hereafter discovered may be used. In one embodiment, the flocculation polymer is a high molecular weight anionic polymer having a molecular weight in excess of about one million. In another embodiment, the flocculation polymer has a molecular weight in the range of about 10 to about 15 million. Exemplary anionic flocculation polymers include, but are not limited to, a copolymer of a polyacrylamide and a polyampholyte. In a further embodiment, the flocculation polymer is a cationic polymer. Exemplary cationic polymers include, without limitation: quaternary polyamines, for example, poly D AD MAC; polyethyleneimine; and polyguanidine. In yet another embodiment, the flocculation polymer is a non- ionic polymer. Exemplary non-ionic polymers include, but are not limited to, acrylamide homopolymers, polyacrylamides, and polyethylene oxides. The flocculation process may comprise at least one of ozoning, leaching (bleaching), filtering, re-dispersing in a makedown tank, and spray-drying. Details of exemplary flocculation processes can be found in U.S. Pat. No. 4,227,920 to Chapman and Anderson, and U.S. Pat. No. 5,685,900 to Yuan et al., which includes ozonation.

[024] The flocculation process may comprise the addition of at least one acid used to effect a pH of the kaolin slurry of from about 2 to about 5.5. Appropriate examples of the at least one acid are now known to the skilled artisan and further acids may be hereafter discovered. In one embodiment, the at least one acid is sulfuric acid. In another embodiment, the pH is from about 2.5 to about 5. In a further embodiment, the pH is from about 3 to about 4.5. In yet another embodiment, the pH is from about 3.5 to about 4.

[025] In yet a further embodiment, the kaolin slurry may undergo a first flocculation and a second flocculation, the second flocculation comprising adding at least one flocculation polymer and alum to the slurry. Unlike the above described selective flocculation that floes impurities to facilitate their removal, the second flocculation step floes the kaolin clay, aiding in the removal of water in any subsequent filtration step.

[026] The methods disclosed herein further comprise filtering the kaolin slurry using at least one membrane filter press. A membrane filter press, as used herein, is a filtration apparatus having at least one inflatable chamber, a filter plate, and at least one filter cloth. Upon inflation, the at least one inflatable chamber presses the face of the filter plate against the filter cake of kaolin forming or disposed thereon, removing water homogenously or substantially homogeneously throughout the filter cake through the at least one filter cloth.

[027] The inflation pressure for the at least one inflatable chamber may be provided by techniques now known or hereafter discovered. In one embodiment, water is used to provide the inflation pressure. In a further embodiment, a fluid other than water is used to provide the inflation pressure. In another embodiment, air is used to provide the inflation pressure.

[028] The at least one inflatable chamber may be made of any compound or compounds now known or hereafter discovered, for example, at least one of polypropylene, rubber, and thermoplastics. The pressure of the at least one membrane filter press may reach up to about 250 psi. In one embodiment, the pressure reaches up to about 200 psi. In a further embodiment, the pressure reaches up to about 150 psi. The number of inflatable chambers may vary according to the volume and solids content of slurry being filtered. In one embodiment, the at least one filter press comprises 6 or less inflatable chambers. More than one membrane filter press may be used in parallel operation to accommodate increased volumes of kaolin slurry.

[029] The thickness of the at least one inflatable chamber may be adjusted to produce a sufficiently dewatered filter cake. In one embodiment, the thickness is less than or equal to about 45 mm. In another embodiment, the thickness is less than or equal to about 35 mm. In a further embodiment, the thickness is less than or equal to about 30 mm. In yet another embodiment, the thickness ranges from about 30 mm to about 40 mm. In yet a further embodiment, the thickness ranges from about 33 mm to about 37 mm.

[030] The composition of the at least one filter cloth, including for example its material, weave, and filament style, may be chosen according to the kaolin slurry and the desired filtration solids amount. Exemplary materials for the at least one filter cloth include, but are not limited to, at least one of polyester, polypropylene, polyethylene, nylon, polyamide 11 , polyamide 12, polyvinylidene fluoride, and polyethylene terephthalate. Exemplary weaves include, but are not limited to, plain, twill, basket, leno, and satin weaves. Exemplary filaments include, but are not limited to, at least one of multifilament yarns, continuous filament yarns, monofilament yarns, and staple yarns.

[031] The resulting filter cake may comprise at least about 60% solids. In one embodiment, the filter cake comprises at least about 62% solids. In another embodiment, the filter cake comprises at least 64% solids. In a further embodiment, the filter cake comprises at least 66% solids. In yet another embodiment, the filter cake comprises from about 60% to about 70% solids. In yet a further embodiment, the filter cake comprises from about 62% to about 68% solids. In still another embodiment, the filter cake comprises from about 64% to about 68% solids. In still a further embodiment, the filter cake comprises from about 66% to about 68% solids.

[032] The filter cakes may exhibit a conductivity ranging from about 100 mS/cm to about 650 mS/cm. In one embodiment, the conductivity ranges from about 200 mS/cm to about 550 mS/cm. In another embodiment, the conductivity ranges from about 300 mS/cm to about 450 mS/cm.

[033] The filter cake may undergo at least one additional processing step. In one embodiment, the at least one additional processing step is re-dispersing the filter cake into an aqueous solution, resulting in a high solids slurry. The high solids slurry may be prepared by adding water and at least one dispersant to the filter cake. Exemplary dispersants include, but are not limited to, sodium polyacrylate, ammonium polyacrylate, sodium hexametaphosphate, tetrasodium pyrophosphate, and sodium silicate. The at least one dispersant may be added to the filter cake slurry in an amount from about 0.25 pounds ("pds")/ton to about 2.0 pds/ton on an active basis. In one embodiment, the at least one dispersant ranges from about 0.5 pds/ton to about 0.7 pds/ton. In a further embodiment, the at least one dispersant is added in an amount of about 0.6 pds/ton. At least one pH regulator may be added to the kaolin cake slurry. Exemplary pH regulators include, but are not limited to, sodium hydroxide and ammonium hydroxide. In one embodiment, the pH of the high solids slurry after the addition of the at least one pH regulatory ranges from about 8 to about 12. In another embodiment, the pH ranges from about 9 to about 11. In a further embodiment, the pH ranges from about 9.5 to about 10.5. Re-dispersing may be aided by the application of mechanical energy. In one embodiment, the filter cake, water, the at least one dispersant, and any optional pH regulator may be agitated in a high-shear mixer, including but not limited to a Waring blender or other suitable mixing apparatus now known to the skilled artisan or hereafter discovered. [034] The high solids slurry resulting from re-dispersing the filter cake may comprise at least about 60% solids. In one embodiment, the high solids slurry comprises at least about 62% solids. In another embodiment, the high solids slurry comprises at least about 64% solids. The high solids slurry may have a low-shear viscosity ranging from about 100 cps to about 120 cps, when measured as Brookfield viscosity at 20 rpm using a #2 spindle. In one embodiment, the low- shear viscosity ranges from about 105 cps to about 115 cps. In another embodiment, the low-shear viscosity ranges from about 108 cps to about 112 cps. The high solids slurry may have a high-shear viscosity ranging from about 4 dynes to about 5 dynes, when measured as Hercules viscosity at 4400 rpm using an "A" bob. In one embodiment, the high-shear viscosity ranges from about 4.2 dynes to about 4.8 dynes. In another embodiment, the high-shear viscosity ranges from about 4.4 dynes to about 4.6 dynes.

[035] The particle size distribution of the re-dispersed filter cake slurry is the same or similar to the particle size distribution of the filter cake feed. In one embodiment, the kaolin particle size distribution of the re-dispersed filter cake slurry may range from 85% to 98% less than 0.5 μm. In another embodiment, the kaolin particle size distribution of the re-dispersed filter cake slurry may range from 85% to 90% less than 0.5 μm. In another embodiment, the d₅₀ of the kaolin particles is less than 0.5 microns. In a further embodiment, the d₅₀ of the kaolin particles is less than 0.3 micron. In yet another embodiment, the d₅o of the kaolin particles is less than 0.2 micron. In yet a further embodiment, the d₅₀ of the kaolin particles is less than 0.15 micron.

[036] In one embodiment, the re-dispersed filter cake slurry may undergo at least one processing steps as described above for the kaolin slurry.

[037] The filter cake or the high solids slurry prepared from the filter cake may be suitable for transport. These filter cakes are useful for transporting as a source of hydrous clay. The filter cakes may also be useful as feed to dryers without first undergoing re-dispersion to a slurry. In one embodiment, the filter cake or the high solids slurry is dried, which allows transport in a substantially dry form. In one such embodiment, the filter cake or high solids slurry is dried by evaporation. In another such embodiment, the filter cake or high solids slurry is thermally dried, such as in a flash dryer, apron dryer, rotary dryer, and the like. In a further such embodiment, the high solids slurry is dried by introducing the slurry into a spray dryer. The moisture content of the spray-dried high solids slurry may be less than about 1 %. In one embodiment, the moisture content is less than about 0.8%. In another embodiment, the moisture content is less than about 0.5%.

[038] In one embodiment, the dried filter cake or the dried high solids slurry is milled. In another embodiment, the dried filter cake or the dried high solids slurry is calcined. For example, calcining may comprise exposing the dried filter cake or the dried high solids slurry to temperatures of about 1000 ⁰C or more for about 30 minutes.

[039] Unless otherwise indicated to the contrary, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification, including claims, are to be understood as being modified in all instances by the term "about." Accordingly, unless otherwise indicated to the contrary, the numerical parameters are approximations and may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should be construed in light of the number of significant digits and ordinary rounding approaches.

[040] Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.

Examples

Example 1

[041] A 34.0% solids diluted slurry was prepared from a 53.5% solids beneficiated kaolin clay slurry and a 4.0-5.0% solids nanodimensional kaolin clay slurry. The particle size of the nanodimensional kaolin clay was consistent with the particle size distribution of INFILM 939 kaolin clay (Imerys Pigments, Inc.; Roswell, Georgia, USA). The particle size distribution of those two feed streams and the resulting diluted slurry are provided in Table 1. The diluted slurry was fed to the MERCO process before undergoing filtration.

Table 1

[042] The MERCO product slurry was then filtered using an ANDRITZ filter (Andritz AG; Graz, Austria) press to investigate the effect of processing variables, as shown in Table 2 . The filter cloth material was PRIMAPOR multifilament polyester cloth (Madison Filter Ltd.; Lancashire, England) having a surface coating designed to capture extremely fine particles.

Table 2

[043] The thickness and solids percentage of the resulting filter cake are provided in Table 3. At membrane pressures between 60 psi and 70 psi, the solids content was at least 60% regardless of the other variables.

Table 3

* Average

[044] The filter cake produced in run 2 had a thickness sufficient to preclude homogenous squeezing. Thickness was measured at various locations of the filter cake and the average provided in Table 3. The thickness of the filter cakes in the other runs were homogenous or substantially homogeneous, and the provided thickness data is indicative of the thickness of the cake in general.

[045] 300 grams of an inventive 62.2% kaolin-clay filter cake, measured on a dry basis, was mixed with a sufficient amount of water to prepare a slurry having 61.8% solids. The slurry was prepared by blending the cake and water in a Waring blender for 3 minutes and was dosed with 0.5 Ib/ton sodium polyacrylate and 6.3 Ib/ton sodium hydroxide. The pH of the resulting slurry was 9.21.

[046] The low-shear viscosity was measured using a Brookfield machine with spindle #2. The low-shear viscosity was 108 cps at 20 rpm and 70 cps at 100 rpm. The high-shear viscosity was measured using a Hercules apparatus with an "A" bob. The high-shear viscosity was 4.31 dynes at 4400 rpm. The particle size distribution was determined using a SEDIGRAPH analyzer (Micromeritics Instruments Corporation, Norcross, GA, U.S.A.) and is provided in Table 4. Table 4

Example 2

[047] A portion of the filter cake slurry from Example 1 was oven-dried at 110 ⁰C overnight. The dried slurry was then calcined at 1 ,080 ⁰C for 30 minutes. The qualities of the calcined-kaolin clay are provided in Table 5. Typical brightness for a calcined kaolin clay is 92. A brightness over 92 indicates a spec quality material.

Table 5

Claims

WHAT IS CLAIMED IS:

1. A method for producing a kaolin-clay filter cake comprising: providing a flocculated kaolin slurry having a kaolin particles solids content of less than about 55% and a kaolin particle size distribution such that at least about 70% by weight of the kaolin particles have a particle size less than about 0.5 microns; and filtering said flocculated kaolin slurry in at least one membrane pressure filter press comprising at least one filter plate, at least one filter cloth, and at least one inflatable chamber, to produce a kaolin-clay filter cake having a solids content of at least about 60%.

2. A method for producing a high solids kaolin slurry, comprising re-dispersing in water a kaolin-clay filter cake made according to the method of claim 1.

3. A method for producing a dried kaolin product, comprising spray-drying a high solids kaolin slurry made according to the method of claim 1.

4. The method according to claim 3, further comprising calcining the spray- dried kaolin.

5. The method according to claim 1 , further comprising drying the filter cake.

6. The method according to claim 1 , further comprising pulverizing the filter cake.

7. The method according to claim 1 , further comprising calcining the filter cake.

8. The method according to claim 1 , wherein the providing step comprises at least one beneficiation step chosen from the group consisting of selective flocculation, ozone treatment, flotation, magnetic separation, and leaching.

9. The method according to claim 1 , wherein the providing step comprises degritting the flocculated kaolin slurry to remove particles greater than about 45 μm.

10. The method according to claim 1 , wherein the flocculated kaolin slurry has a solids content of less than about 50%.

11. The method according to claim 10, wherein the flocculated kaolin slurry has a solids content of less than about 45%.

12. The method according to claim 11 , wherein the flocculated kaolin slurry has a solids content of less than about 40%.

13. The method according to claim 1 , wherein at least about 85% by weight of the kaolin particles have a particle size less than about 0.5 microns.

14. The method according to claim 13, wherein at least about 95% by weight of the kaolin particles have a particle size less than about 0.5 microns.

15. The method according to claim 14, wherein at least about 98% by weight of the kaolin particles have a particle size less than about 0.5 microns.

16. The method according to claim 1 , wherein about 70% by weight to about 98% by weight of the kaolin particles have a particle size less than about 0.5 microns.

17. The method according to claim 16, wherein about 85% to about 98% by weight of the kaolin particles have a particle size less than about 0.5 microns.

18. The method according to claim 1 , wherein the d₅₀ of the kaolin particles is less than about 0.5 microns.

19. The method according to claim 18, wherein the d₅o of the kaolin particles is less than about 0.3 microns.

20. The method according to claim 19, wherein the d₅o of the kaolin particles is less than about 0.2 microns.

21. The method according to claim 1 , wherein the flocculated kaolin slurry comprises at least one dispersing agent chosen from the group consisting of sodium polyacrylate, sodium hexametaphosphate, tetrasodium phosphate, sodium silicate, and ammonium polyacrylate.

22. The method according to claim 1 , wherein the pH of the flocculated kaolin slurry ranges from about 2 to about 5.5.

23. The method according to claim 22, wherein the pH of the flocculated kaolin slurry ranges from about 2.5 to about 5.

24. The method according to claim 1 , wherein the pH of the flocculated kaolin slurry is adjusted by the addition of sulfuric acid.

25. The method according to claim 1 , wherein the solids content of the filter cake is at least about 62%.

26. The method according to claim 25, wherein the solids content of the filter cake is at least about 64%.

27. The method according to claim 26, wherein the solids content of the filter cake is at least about 66%.

28. The method according to claim 1 , wherein the solids content of the filter cake is no more than about 70%.

29. The method according to claim 28, wherein the solids content of the filter cake is no more than about 68%.

30. The method according to claim 1 , wherein the pressure of the at least one membrane pressure filter press is equal to or less than about 250 psi.

31. The method according to claim 30, wherein the pressure of the at least one membrane pressure filter press is equal to or less than about 200 psi.

32. The method according to claim 30, wherein the pressure of the at least one membrane pressure filter press is equal to or less than about 150 psi.

33. The method according to claim 1. wherein the thickness of the at least one inflatable chamber is equal to or less than about 45 mm.

34. The method according to claim 33, wherein the thickness of the at least one inflatable chamber is equal to or less than about 35 mm.

35. The method according to claim 34, wherein the thickness of the at least one inflatable chamber is equal to or less than about 30 mm.

36. The method according to claim 1 , wherein the at least one filter cloth is chosen from the group consisting of polypropylene, polyethylene, nylon, polyester, polyamide 11 , polyamide 12, polyvinylidene fluoride, and polyethylene terephthalate.

37. The method according to claim 36, wherein the at least one filter cloth is polyester.

38. The method according to claim 1 , wherein the at least one filter cloth comprises filaments chosen from at least one of the group consisting of multifilament yarns, continuous filament yarns, monofilament yarns, and staple yarns.

39. The method according to claim 1 , wherein the at least one filter cloth comprises a at least one weave chosen from the group consisting of plain, twill, basket, leno, and satin.

40. The method according to claim 1 , wherein the at least one inflatable chamber is made from at least one of the group consisting of polypropylene, rubber, and thermoplastic.

41. The method according to claim 2, wherein the re-dispersing step comprises adding alum and at least one dispersant to the mixture of filter cake and water.

42. The method according to claim 41 , wherein the at least one dispersant is chosen from the group consisting of sodium polyacrylate, sodium hexametaphosphate, tetrasodium phosphate, sodium silicate, and ammonium polyacrylate.

43. The method according to claim 41 , wherein the at least one dispersant is added in an amount ranging from about 0.25 Ib to about 2.0 Ib per ton of kaolin clay.

44. The method according to claim 43, wherein the at least one dispersant is added in an amount ranging from about 0.4 Ib to about 0.8 Ib per ton of kaolin clay.

45. The method according to claim 2, wherein the pH of the high solids kaolin slurry ranges from about 8 to about 12.

46. The method according to claim 45, wherein the pH of the high solids kaolin slurry ranges from about 9 to about 11.

47. The method according to claim 46, wherein the pH of the high solids kaolin slurry ranges from about 9.5 to about 10.5.

48. The method according to claim 2, wherein the high solids kaolin slurry has a high-shear viscosity ranging from about 4 dynes to about 5 dynes, when measured using a Hercules viscometer with an "A" bob at 4400 rpm.

49. The method according to claim 48, wherein the high solids kaolin slurry has a high-shear viscosity ranging from about 4.2 dynes to about 4.8 dynes, when measured using a Hercules viscometer with an "A" bob at 4400 rpm.

50. The method according to claim 49, wherein the high solids kaolin slurry has a high-shear viscosity ranging from about 4.4 dynes to about 4.6 dynes, when measured using a Hercules viscometer with an "A" bob at 4400 rpm.

51. The method according to claim 2, wherein the high solids kaolin slurry has a low-shear viscosity ranging from about 100 cps to about 120 cps, when measured using a Brookfield viscometer with a #2 spindle at 20 rpm.

52. The method according to claim 51 , wherein the high solids kaolin slurry has a low-shear viscosity ranging from about 105 cps to about 115 cps, when measured using a Brookfield viscometer with a #2 spindle at 20 rpm.

53. The method according to claim 52, wherein the high solids kaolin slurry has a low-shear viscosity ranging from about 108 cps to about 112 cps, when measured using a Brookfield viscometer with a #2 spindle at 20 rpm.

54. The method according to claim 2, wherein the high solids kaolin slurry comprises at least about 60% solids.

55. The method according to claim 2, wherein about 88% to about 90% of the kaolin particles in the high solids kaolin slurry has an esd of less than about 0.5 μm.

56. The method according to claim 3, wherein the moisture content of the dried kaolin product is less than about 1 %.

57. The method according to claim 56, wherein the moisture content of the dried kaolin product is less than about 0.8%.

58. The method according to claim 57, wherein the moisture content of the dried kaolin product is less than about 0.5%.

59. A kaolin-clay filter cake comprising at least about 60% solids, and having a kaolin particle size distribution such that at least about 85% by weight of the kaolin particles have a particle size less than about 2 microns.

60. The kaolin-clay filter cake according to claim 59, comprising at least about 62% solids.

61. The kaolin-clay filter cake according to claim 60, comprising at least about 64% solids.

62. The kaolin-clay filter cake according to claim 59, comprising no more than about 70% solids.

63. A kaolin-clay filter cake made by a method comprising: providing a flocculated kaolin slurry having a kaolin particles solids content of less than about 55% and a kaolin particle size distribution such that at least about 70% by weight of the kaolin particles have a particle size less than about 2 microns; and filtering said flocculated kaolin slurry in at least one membrane pressure filter press comprising at least one filter plate, at least one filter cloth, and at least one inflatable chamber, to produce a kaolin-clay filter cake having a solids content of at least about 60%.