WO2008102158A1

WO2008102158A1 - Treatment of white inorganic mineral ores

Info

Publication number: WO2008102158A1
Application number: PCT/GB2008/000621
Authority: WO
Inventors: Jacek Antoni Kostuch; Desmond Charles Payton; Mikko Henrik Likitalo
Original assignee: Imerys Minerals Ltd
Current assignee: Imerys Minerals Ltd
Priority date: 2007-02-23
Filing date: 2008-02-22
Publication date: 2008-08-28
Anticipated expiration: 2009-08-23
Also published as: GB0703634D0

Abstract

The present invention provides an integrated process for treating an ore of a white inorganic mineral to produce a product having improved optical properties, said process comprising: a) providing said ore of a white inorganic mineral and physically separating the ore into a brighter fraction and a darker fraction, said darker fraction comprising discolouring impurities; b) dry crushing and/or grinding the brighter fraction; c) dry crushing and/or grinding the darker fraction and preparing an aqueous slurry of the resulting crushed and/or ground darker fraction; d) beneficiating the darker fraction obtained in (c) to remove at least some of the discolouring impurities; e) optionally, dewatering the beneficiated darker fraction obtained in (d); f) optionally combining at least a portion of the beneficiated darker fraction obtained in (d) or the dewatered beneficiated darker fraction obtained in (e) with at least a portion of the dry ground brighter fraction obtained in (b) to form said product having improved optical properties.

Description

TREATMENT OF WHITE INORGANIC MINERAL ORES

Field of the Invention

This invention is concerned with processes for treating ores of white inorganic minerals, including ores comprising alkaline earth metal carbonates, particularly calcium carbonate, in order to produce products having improved optical properties. These products are also suitable for further processing in order to make final products. The present invention is also concerned with systems for performing said processes.

Background of the Invention

White minerals, such as calcium carbonate, may be used as pigments and/or fillers in various products, including in paper, paper coatings, polymer compositions (e.g. plastics), and surface coatings, such as paints and film laminates. A high degree of whiteness and/or brightness of minerals, such as calcium carbonate, are often desirable for use in these products.

Inorganic minerals may be obtained from a variety of sources. For example, calcium carbonate may be obtained from a natural source by grinding (GCC), or may be prepared synthetically by precipitation (PCC).

High brightness PCC is produced by chemical processes, which are comparatively complex. Ground calcium carbonate may comprise ground naturally occurring calcium carbonates obtained from known sources, including marble, limestone and chalk. These sources of calcium carbonate are abundant in numerous parts of the world, and therefore represent a ready source of raw materials. In practice, however, it is found that many natural deposits are so highly contaminated with discolourants that, when comminuted in their natural state, they are unacceptable as fillers or pigments.

Methods for improving the brightness and/or whiteness of processed minerals such as GCC are known in the art, and include froth flotation, magnetic separation, bleaching, leaching and electrostatic sorting. As a result of the widely varying levels of contamination in mineral ores, known treatments, including beneficiation processes, are not necessarily effective or energy efficient in a wide variety of circumstances.

The object of the present invention is to provide at least an alternative method of treating white inorganic mineral ores in order to provide products with improved optical properties, by, for example, increasing the brightness and/or whiteness thereof. Broadly, this objective is addressed by a process which comprises physically separating a substantially brighter or whiter portion of a white mineral ore from a substantially darker portion, followed by the treatment of an aqueous slurry of the darker portion in order to, for example, increase its brightness and/or whiteness. The fractions may, optionally, be recombined, thus, advantageously reducing the need to dewater the treated darker fraction. This approach increases the overall recovery from the raw material, thus providing a more environmentally friendly and sustainable option.

Summary of the Invention

According to the present invention, in a first aspect, there is provided an integrated process for treating an ore of a white inorganic mineral to produce a product having improved optical properties, said process comprising:

a) providing said ore of a white inorganic mineral and physically separating the ore into a substantially dry brighter fraction and a substantially dry darker fraction, said darker fraction comprising discolouring impurities; b) dry crushing and/or grinding the substantially dry brighter fraction; c) dry crushing and/or grinding the substantially dry darker fraction and preparing an aqueous slurry of the resulting crushed and/or ground substantially dry darker fraction; d) beneficiating the darker fraction obtained in (c) to remove at least some of the discolouring impurities; e) optionally, dewatering the beneficiated darker fraction obtained in (d); f) optionally combining at least a portion of the beneficiated darker fraction obtained in (d) or the dewatered beneficiated darker fraction obtained in (e) with at least a portion of the dry ground brighter fraction obtained in (b) to form said product having improved optical properties. In a) the separated fractions may be formed on the basis of whiteness with the less white fraction being subjected to the beneficiation process in (d). By improving the optical properties of the ore, there results an increase in whiteness and/or brightness.

The dry brighter (and/or whiter) fraction obtained in b) may be processed separately to form one or more final products. The treated darker fraction obtained in d) or e) may be processed separately in order to form one or more final products. The product or products obtained in b), d) and e) may be referred to as an intermediate product or collectively as intermediate products. Preferably the separated fractions are at least partially re-combined following treatment. One particular advantage associated with this recombination of the treated fractions in f) is that it reduces the requirement to dewater the treated darker fraction and thus provides a more energy efficient process overall. In addition, the costs associated with treating the darker fraction are correspondingly less when compared to treatment of the unseparated ore. These reductions in cost may be a result of one or more of: reduced chemical demand; a decrease in the amount of energy required; and a higher product recovery. The product formed in f) may be referred to as the lump or granulate product. The precise form of the lump or granulate product will depend at least to some extent on the technology used to combine the two streams.

In c), the substantially dry darker fraction may be wet ground following dry crushing and/or dry grinding.

According to a further aspect of the present invention, there is provided the final products of the further processing of the product(s), including the intermediate products obtained according to the first aspect of the present invention. These final products of the invention include paper products which include fillers and coating formulations, inks, rubber products, paint compositions (matt and glossy), polymer products, ceramics, barrier coatings. The term paper products should be understood to mean all forms of paper, including board, card, paperboard, and the like.

The products from b), d), e) and/or f) may be split and transported to a plurality of locations proximate to end users for additional processing to produce multiple final products having characteristics tailored to the needs of each end-user. As such, said products may be further processed at a second location to produce a particulate white inorganic mineral having a desired particle size distribution. According to a yet further aspect of the present invention, there is provided an integrated system for carrying out the process according to the first aspect of the invention comprising:

I. a device, e.g. an optical sorter, for physically separating the ore into a substantially dry brighter (and/or whiter) fraction and substantially dry darker (and/or less white) fraction;

II. a crusher and/or grinder for comminuting the substantially dry brighter (and/or whiter) fraction;

III. a crusher and/or grinder, for comminuting the substantially dry darker fraction;

IV. a source of water for preparing an aqueous slurry of the comminuted darker fraction;

V. means for treating the aqueous slurry of the ground darker fraction; Vl. optionally, a dewatering device for dewatering the beneficiated darker fraction;

VII. optionally, means for combining at least a portion of the treated fractions.

The substantially dry fractions formed in a) in the first aspect of the invention or by I. in the system, typically contain less than about 5wt% moisture, for example less than about 2wt% moisture.

The system may also comprise a grinder for grinding the aqueous slurry of the comminuted darker fraction in IV.

Unless otherwise stated, the mean (average) equivalent particle diameter (d₅₀ value) and other particle size properties referred to herein for the inorganic particulate materials are as measured in a well known manner by sedimentation of the particulate material in a fully dispersed condition in an aqueous medium using a Sedigraph 5100 machine as supplied by Micromeritics Instruments Corporation, Norcross, Georgia, USA (telephone: +1 770 662 3620; web-site: www.micromeritics.com), referred to herein as a "Micromeritics Sedigraph 5100 unit". Such a machine provides measurements and a plot of the cumulative percentage by weight of particles having a size, referred to in the art as the 'equivalent spherical diameter' (esd), less than given esd values. The mean particle size d₅₀ is the value determined in this way of the particle esd at which there are 50% by weight of the particles which have an equivalent spherical diameter less than that d₅₀ value. Detailed Description of the Invention

The White Inorganic Mineral Ore

The raw material for use in the present invention is a substantially dry white mineral ore, such as a dry ore comprising an alkaline earth metal carbonate. The substantially dry white mineral ore typically contains less than about 5wt% moisture, for example less than about 2wt% moisture.

In particular, the dry ore may be a calcium carbonate containing ore from one or more of the known natural sources, including marble, limestone or chalk. The dry ore may contain discolouring impurities such as pyrites, mica, graphite, chlorite, iron oxides, zinc sulphide, manganese oxides and other coloured minerals typically associated with calcium carbonate ores. The total content of discolouring impurities can be as high as about 15wt%. However, typically the total content of discolouring impurities is less than about 2wt%.

The ore is provided as particulate matter, where the largest particles may have a diameter, for example, ranging from about 1 mm to about 120mm. For example, the particles may have diameters between about 10 mm and about 120 mm.

Hereafter, the invention may tend to be discussed in terms of a feed comprising calcium carbonate, and in relation to aspects where the calcium carbonate is processed and/or treated. The invention should not be construed as being limited to such embodiments.

The Separating Process

The white inorganic mineral ore may be separated on the basis of colour including whiteness and/or brightness.

The separating process may be an essentially manual process and simply involve one or more persons visually inspecting the ore and separating the material by hand. However, more typically, the separating process will be automated and make use of one or more sensors to detect a suitable characteristic or physical property of the particles of the ore to be separated which is then used to trigger a physical separation of the ore particles into suitable fractions. Suitable systems for use in the present invention are made by Mogensen (www.mogensen.de), including the Mogensen MikroSort® system which is suitable, inter alia, for use in detecting slight differences in colour, brightness and shade of minerals such as limestone.

One way of separating the particles of the ore into separate fractions is with the use of one or more fluid streams. The one or more fluid streams may comprise a gas and/or a liquid. The fluid stream may be activated or triggered by a particle possessing a particular physical property passing a sensor. When the measurable property is sensed, it triggers a fluid stream to be activated and to impinge upon the targeted particle to separate it from the main body of the ore. In order to trigger a response, the one or more sensors may be linked to one or more actuators which may be double acting. The one or more sensors, or sensor system, may include appropriate electrical circuits for detecting the responses of the respective sensing elements upon detection of a desired particle and for translating such signals into respective gating signals timed to actuate the selection system at the appropriate instance and to allow or enable return of the selection system to its normal state following the selection. A suitable system and circuitry are described in US 3472375, the contents of which are hereby incorporated by reference in their entirety.

For example, US 3722676 and references therein, the contents of which are hereby incorporated in their entirety by reference, describe methods for physically separating solid particles of a first type from particles of a second type. Such a method is suitable for use in the present invention. The separation can be based on measurable physical properties of the particles contained in the fractions, such as their colour. More specifically, the device or apparatus described in US 3722676 includes a plurality of selectively deflectable flowing fluid streams. The streams are controlled to displace the desired mineral particles from the ore. Pivotally mounted arcuate tubs may be used to divert the fluid streams when they are not acting to displace particles and these tubes are selectively movable to allow the streams to hit desired particles. A screen may be used for conveying the ore past the fluid streams in such a manner that the streams may act through the screen to displace the selected particles.

The material to be separated may be conveyed past one or more sensors, which detect the desired characteristic of the desired particles. Suitable sensors include colour sensors, reflectivity sensors and any sensor suitable to bring about the desired result of a separation of the ore into a substantially brighter and/or whiter fraction from a darker or less white fraction. In order to achieve a separation based on brightness and/or whiteness, it may not be necessary to directly measure these properties.

In the Mikrosort® systems mentioned previously, the material to be separated is loosened and fed to a chute where it may be scanned by one or more colour line cameras across the whole working width. The scanned images may be evaluated by a parallel-working computer which may address compressed air valves in a controlled way which blow off the targeted particles.

For the purposes of the present invention, fluids used to separate the material may include liquids and/or gases.

The system according to the present invention may be calibrated so that the separated fractions are determined by selecting a particular value in connection with the physical characteristic to be measured. For example, the system may be arranged so that the darker fraction substantially comprises particles possessing a brightness, of < 95 ISO, for example < 92 ISO when the material is ground to substantially 90wt% finer than 2μm.

The difference in brightness, when the stream is ground to substantially 90wt% finer than 2μm, between the brighter and darker fractions prior and during separation may typically be at least 1 point on the ISO brightness scale, for example, at least 3 points. For example, the ISO brightness of the brighter fraction may be greater than or about one point higher, preferably greater than or about two points higher, preferably greater than or about three points higher.

The ISO brightness, as expressed herein, refers to the percentage reflectance to light of a 457nm wavelength.

The whiteness referred to herein is measured according to the CIE standard codified by ISO 11475:1999 and Determination of CIE whiteness, D65/10 degrees (outdoor daylight). The Brighter (and/or whiter) Fraction

Dry Crushing/ Grinding

The brighter (and/or whiter) fraction of the mineral ore is ground using a dry grinding process. Dry grinding processes are well known in the art. There are various known techniques which are well known to the skilled person and suitable for use in the present invention for producing a crushed or ground product possessing a nominal particle size of about 1 mm to about 2mm.

For example, ground calcium carbonate (GCC) is typically obtained by grinding a mineral source such as chalk, marble or limestone which may be followed by a particle size classification step in order to obtain a product having the desired degree of fineness. The grinding process is carried out in a dry state ("dry grinding"), in the absence of added hygroscopic or hydrophilic chemicals. This ensures that the surfaces of the ground particles are "clean", and do not have adhering to them any of the chemicals which may be used in a wet grinding process. By "dry grinding" herein, we mean that the grinding process is carried out in the presence of 10% or less water.

The Darker Fraction

Crushing/Grinding

The darker fraction of the mineral ore may be ground using a wet grinding process following substantially dry crushing. Initially the material may be crushed using a combined hammer-type mill closely coupled with a 'wipe-through' screen which produces a stream of particles of about 1-2mm. This material may be directly fed to a close-coupled autogenous stirred grinder. Depending on the crystallinity of the raw material, synthetic media may be required in order to increase the grinding efficiency. The wet grinding may be carried out with about at least 30wt% water present, for example about 50wt% water present and may be as high as about 70 wt%. At high solids grinding, for example around 70wt%, the use of one or more dispersants is preferred, Suitable dispersants for use in the present invention, and amounts thereof, are well known to the skilled person and include appropriate amounts of sodium polyacrylate. As a result of the grinding process, the darker fraction may have a particle size distribution of about 30% by weight less than about 2 μm; for example, between about 20% and 35% by weight of particles below about 2 μm, more preferably between about 20% and 30% by weight of particles below about 2 μm, based on the dry weight of the white inorganic mineral.

Removal of discolouring impurities

The removal of the discolouring impurities can be carried out in a number of ways, all well known to the skilled person.

Known beneficiation methods include froth flotation and magnetic separation of the discolouring particles in the slurry. Other suitable techniques for removing discolouring impurities include bleaching, leaching or electrostatic sorting.

US 5084254, and references therein, the entire contents of which are incorporated herein by reference, describes a process for purifying calcium carbonate which comprises the use of froth flotation. These techniques are suitable for use in the present invention. Typical discolouring impurities which may be removed include graphite, bituminous organic materials, iron containing compounds such as pyrites and other iron stained minerals.

As such, the beneficiation in d) according to the first aspect of the present invention may comprise subjecting the calcium carbonate slurry to froth flotation using a collector for discolouring impurities. The collector may comprise a cation comprising at least one long chain alkyl group having from 10 to 24 carbon atoms. This yields an underflow product comprising the calcium carbonate from which substantially all of the discolouring impurities have been removed. Useful collector agents may include xanthates such as potassium ethyl xanthate, various hydrocarbons including kerosene, fuel oil, mineral oils, or mineral oil fractions, as well as aromatic hydrocarbons such as dipentine or other collectors as are known in the art. Similarly, frothers such as pine oil, cresylic acid, polypropylene glycol ether or other well-known agents of this type may be utilised. Suitable methods for carrying out froth flotation are also described in US 4165840 and references therein, the contents of which are hereby incorporated in their entirety.

When magnetic separation is used to remove discolouring impurities, the aqueous slurry, which may or may not be dispersed, may be introduced into a magnetic field of sufficient field strength to magnetise ferric components in the slurry. The aqueous slurry may then be removed from the magnetic field and placed in sufficiently close proximity to a magnetic or magnetisable material so that the said ferric components of the dispersion are concentrated in the vicinity of the magnetic or magnetisable material. The concentrated ferric components may then be separated from the remainder of the slurry.

Suitable dispersing agents may be used if desired. The magnetic field may be produced by any suitable means. For example, the magnetic field may be produced by an electromagnet such as a super-conducting magnet. The magnetic field may have a field strength of greater than about 1 Tesla, for example greater than about 2 Tesla, for example greater than about 3 Tesla, for example greater than about 4 Tesla, for example less than about 7 Tesla. Preferably, the magnetic field strength is about 5 Tesla. The magnetic field is of sufficient strength to magnetise magnetisable particles in the aqueous slurry. The magnetisation effect may be of permanent or temporary effect.

The aqueous slurry may be static in the magnetic field or may be passed through the magnetic field in a flow. Where a flow system is used, the flow may take place at any suitable rate, and in any suitable way. For example, the aqueous slurry may be passed through the magnetic field at a flow rate of greater than about 10ml s^"1, for example greater than about 15ml s^"1, for example greater than about 20ml s^"\ for example about 25ml s \

The magnetic or magnetisable material may suitably be a ferromagnetic material of any suitable type and in any suitable configuration. For example, the ferromagnetic material may comprise iron, nickel, cobalt or any combination thereof. For example, the ferromagnetic material may be an alloy comprising iron, nickel, cobalt or any combination thereof. The alloy may also comprise other materials, for example carbon. The ferromagnetic material may preferably be formed into any suitable arrangement for contacting with the magnetised aqueous slurry such that the magnetised particles in the dispersion adhere magnetically to the ferromagnetic material. Arrangements which result in a large contact surface area between the dispersion and the ferromagnetic material are therefore particularly favoured. For example, the ferromagnetic material may be in the form of a sieve or mesh or a plurality of sieves and/or meshes. For example, a packed bed may be used comprising particles which comprise a ferromagnetic material, for example particles which are coated with a ferromagnetic material, for example particles which consist essentially of a ferromagnetic material. For example, the ferromagnetic material may be disposed as elongate elements, whose length may be substantially greater than their greatest transverse dimension. The elongate elements may be in an ordered arrangement, for example woven, coiled and/or aligned, or a disordered arrangement, for example entangled and/or matted.

The step of placing the aqueous slurry in sufficiently close proximity to a magnetic or magnetisable material so that the said ferric components of the slurry are concentrated in the vicinity of the magnetic or magnetisable material may be carried out in a static or moving arrangement. The moving arrangement involves relative movement of the aqueous slurry and the magnetic or magnetisable material, although it is not necessary that both are individually moving. It is preferred that the aqueous slurry is moving and the magnetic or magnetisable material is static. It is preferred that the aqueous slurry is in direct contact with the magnetic or magnetisable material in a container or apparatus.

After the ferric components of the aqueous slurry have been concentrated as described above, the ferric components are separated from the remainder of the aqueous slurry. In the preferred arrangement described above, the ferric-depleted aqueous slurry flows on and away from the ferric components adhered to the magnetic or magnetisable (e.g ferromagnetic) material.

The ferric components may subsequently be removed from the ferromagnetic material by any suitable means. The magnetised particles may be removed by mechanical agitation, or by thermal treatment or by contacting the ferromagnetic material to which the magnetised particles have adhered with a suitable liquid wash, for example water.

Preferably, the magnetised particles are magnetised temporarily such that they adhere to the ferromagnetic material during the contacting of the dispersion with the ferromagnetic material but become disadhered easily after the contacting has been completed. The ferromagnetic material may be disposed in any suitable vessel. The vessel may, for example, itself be of a ferromagnetic material. The vessel may be provided with inlets and outlets and appropriate valves and control mechanisms as may be required to facilitate the beneficiation process. For example, the vessel may have an inlet and an outlet. The inlet and/or the outlet may be provided with a valve or other means for controlling the flow rate of material through the vessel. The valve(s) or other means may be adapted to be controlled remotely, for example by electronic or computer control equipment.

A particular example of magnetic separation is described in US 3627678, the contents of which are hereby included in their entirety by reference. As such, the aqueous slurry may be subjected to a high intensity magnetic field by passing through a steel wool matrix maintained in a magnetic field of about 7 to 22 kilogauss average intensity, more preferentiality of about 15 to 20 kilogauss. Within the limits of magnetic separator technology used, higher limits may also be used with the invention. The slurry may be passed through the matrix at such a rate so that it is maintained in the magnetic field for at least about 15 seconds, more preferentially between about 30 seconds and 120 seconds. Subject to the effect on processing rates, longer retention times may also be acceptable, and can occur either via a single pass or via cumulative passes through the matrix. The slurry, as passed through the magnetic separator, typically includes from about 20% to 70% solids (by weight), more typically from about 20% to 40%. The matrix material, as known in the art, preferably comprises a packed stainless steel wool, although other filamentary or strandlike materials may be effectively used for this purpose, as may matrices of steel balls, tacks or other slurry-pervious ferromagnetic materials.

The darker fraction may be subjected to bleaching. Suitable techniques and bleaches for bleaching inorganic minerals are well known in the art. Typically one or more bleaches are combined with an aqueous slurry of the inorganic mineral to be bleached.

The calcium carbonate may be subjected to reductive bleaching. Suitable bleaches for reductive bleaching include effective amounts of hydrosulfites such as sodium hydrosulfite and zinc hydrosulfite. Other suitable reductive bleaches include sodium dithionite (also known as sodium hydrosulphite or "Hydros") or formamidine sulfinic acid (FAS, - also known as thiourea dioxide). Other suitable bleaching techniques include the use of combinations of bleaches, such as formamidine sulfinic acid and a borohydride (e.g. sodium borohydride). Preferably the combined use of these bleaches is carried out under alkaline conditions.

The mineral is typically present at a solids content of from about 15wt% to about 80wt%, such as from about 20wt% to about 75wt% or about 40wt% to about 70wt%. The bleach or bleaches may be combined with the inorganic mineral in various forms, including in aqueous solution.

The borohydride may be chosen from the various salt forms, including sodium borohydride. The effective amount of the sodium borohydride included in the mineral slurry is typically at least 5ppm on a dry basis. For example, about 20ppm to about 1000ppm, e.g. about 30ppm to about 120ppm, e.g. about 50ppm to about 500ppm. The effective amount of the FAS included in the slurry may be about 125ppm to about 2500ppm on a dry basis.

The bleaching reaction may be carried out a suitable temperature, e.g. room temperature (2O⁰C) or lower or relatively higher temperatures e.g. at least about 5O⁰C. The temperature of the bleaching reaction may be carried out a temperature from about 5O⁰C to about 9O⁰C. The time for the reductive reaction may range from a few minutes, e.g. about 5 minutes, to a number of hours such as about 24 hours, e.g. about 30 minutes to 60 minutes.

The difference in brightness between the untreated and treated darker fractions when ground to substantially 90wt% finer than 2μm, will typically be at least half a point. For example, the ISO brightness of the treated darker fraction, when ground to substantially 90wt% finer than 2μm, may be greater than or about one point higher, preferably greater than or about two points higher, preferably greater than or about three points higher.

Dewatering

The treated aqueous slurry formed in d) may be dewatered to obtain a concentrated slurry which may have a high solids content of between about 60wt% and 80wt%, more preferably between about 68wt% to 78wt% e.g. about 70wt% and 75wt%. Dewatering can be accomplished by conventional devices known in the art, including through use of pressure filtration, e.g. a filter press or centrifuges or evaporation, e.g. forced evaporation under reduced pressure or centrifugation.

Dewatering of aqueous slurries is a well known procedure and typically used to facilitate storage and transport of the resulting suspension or for use in a high solids application, e.g. as a pigment, filler or extender composition in paper making, paper coating or in plastics or paint compositions.

In processes of this kind it is conventional to avoid use of a dispersing agent in the dewatering step because concentration is carried out with the particulate solids in a flocculated state. After dewatering, the concentrated inorganic particulate material obtained, e.g. a high solids filter cake may comprise a flocculated body whose constituent particle require redispersion.

Combining the Fractions

The product having improved optical properties made according to the first aspect of the present invention may be formed by recombining the aqueous slurry with the dry ground brighter mineral fraction. This product has a moisture content typically of between about 10% and about 15wt%.

This product obtained in f) may conveniently be referred to as the lump or granulate product and is suitable for transportation and/or further processing to form final products. The product formed in f) may be formed by combining the fractions in a granulator or the fractions may be forced through a die to form a pellet of substantially uniform moisture.

Further Processing of the Product(s)

One or more of the various intermediate products and the lump product obtained according to the present invention may be further processed by conventional grinding to produce one or more final products having a desired particle size.

The various products are well suited for transport via any of the generally known methods of transport for transporting minerals and/or mineral slurries, including by ship, truck or rail. This means that further processing of the various products may be carried out on a different site from where the original products were formed.

For example, the products may be further treated at a paper mill to form an aqueous paper coating composition. Also, they may be used on site at manufacturing plants in the manufacturing process of final products.

As such and according to a further aspect of the present invention, there is provided the final products of the further processing of the products obtained according to the first aspect of the present invention. These final products of the invention will be readily apparent to persons skilled in the art and include paper products including fillers and coating formulations, inks, rubber products, paint compositions, polymer products, ceramics, barrier coatings. Calcium carbonate is a well known filler for many applications, partly because of its low cost. Suitable final products in which the calcium carbonate, produced according to the present invention, may be included will be readily apparent to the skilled person where issues such as low cost, enhanced optical properties and efficient filling are relevant.

These final products may be formed from the product of the first aspect of the invention from b) and/or d) and/or e) and or f). Particularly advantageously, the final products are formed from the lump or granulate product formed in f).

(I) Paper products

The term paper products should be understood to mean all forms of paper, including board, card, paperboard, and the like.

The products produced according to the present invention may be blended in various proportions with conventional filler materials, e.g. precipitated or ground calcium carbonate, kaolin and other clay minerals, metakaolin, talc, calcium sulphate, the ingredients and composition being selected according to the quality of the paper required to be produced. In general, these materials are likely to be in a slurry form when they are mixed.

The products can be used in the preparation of a paper making composition or a paper coating composition. The paper making composition may typically comprise, in aqueous suspension, cellulosic fibres and other conventional additives known in the art. A typical paper making composition would typically contain up to about 67% by weight of dry filler material based on the dry weight of the paper making fibres and may also contain a cationic or an anionic retention aid in an amount in the range from 0.1 to 2% by weight, based on the dry weight of the filler material.^' It may also contain a sizing agent which may be, for example, a long chain alkylketene dimer, a wax emulsion or a succinic acid derivative. The composition may also contain dye and/or an optical brightening agent.

A paper coating composition may also comprise, in aqueous or non-aqueous suspension, and in addition to the products made according to the present invention, other filler materials, a binder chosen from binders conventionally used in the art. Exemplary binders include but are not limited to adhesives derived from natural starch and synthetic binders. The formula of the paper coating composition will depend upon the purpose for which the coated paper is to be used, for example, either for offset or gravure printing. Generally speaking, the amount of adhesive will be in the range from 3 to 35% by weight of adhesive solids, based on the dry weight of the coating. There may also be present from 0.01 to 0.5% by weight, based on the dry weight of the coating, of a dispersing agent. Sufficient alkali will generally be added to raise the pH to about 8-9. The adhesive solids may be a starch, a water dispersible synthetic resin or latex such as a styrene butadiene copolymer, a polyvinyl alcohol an acrylic, polyvinyl acetate, a butadiene-acrylonitrile copolymer, a cellulose derivative such as methyl cellulose, sodium carboxymethyl cellulose or hydroxyethyl cellulose or a proteinaceous material such as casein, animal glue or a vegetable protein. Paper coatings may include the products in an amount ranging from about 3% to about 89% by weight on a dry coating basis.

Calendering is a well known process in which paper smoothness and gloss is improved and bulk is reduced by passing a coated paper sheet between calender nips or rollers one or more times. Usually, elastomer coated rolls are employed to give pressing of high solids compositions. An elevated temperature may be applied. One or more (e.g. up to about 12, or sometimes higher) passes through the nips may be applied.

Methods of coating paper and other sheet materials, and apparatus for performing the methods, are widely published and well known. Such known methods and apparatus may conveniently be used for preparing coated paper. For example, there is a review of such methods published in Pulp and Paper International, May 1994, page 18 et seq. Sheets may be coated on the sheet forming machine, i.e., "on-machine," or "off- machine" on a coater or coating machine. Use of high solids compositions is desirable in the coating method because it leaves less water to evaporate subsequently. However, as is well known in the art, the solids level should not be so high that high viscosity and leveling problems are introduced. The methods of coating may be performed using apparatus comprising (i) an application for applying the coating composition to the material to be coated; and (ii) a metering device for ensuring that a correct level of coating composition is applied. When an excess of coating composition is applied to the applicator, the metering device is downstream of it. Alternatively, the correct amount of coating composition may be applied to the applicator by the metering device, e.g., as a film press. At the points of coating application and metering, the paper web support ranges from a backing roll, e.g., via one or two applicators, to nothing (i.e., just tension). The time the coating is in contact with the paper before the excess is finally removed is the dwell time - and this may be short, long or variable. ^"

The coating is usually added by a coating head at a coating station. According to the quality desired, paper grades are uncoated, single coated, double coated and even triple coated. When providing more than one coat, the initial coat (precoat) may have a cheaper formulation and optionally less pigment in the coating composition. A coater that is applying a double coating, i.e. a coating on each side of the paper, will have two or four coating heads, depending on the number of sides coated by each head. Most coating heads coat only one side at a time, but some roll coaters (e.g., film press, gate roll, size press) coat both sides in one pass.

Examples of known coaters which may be employed include, without limitation, air knife coaters, blade coaters, rod coaters, bar coaters, multi-head coaters, roll coaters, roll/blade coaters, cast coaters, laboratory coaters, gravure coaters, kisscoaters, liquid application systems, reverse roll coaters, curtain coaters, spray coaters and extrusion coaters.

Water may be added to the solids comprising the coating composition to give a concentration of solids which is preferably such that, when the composition is coated onto a sheet to a desired target coating .weight, the composition has a rheology which is suitable to enable the composition to be coated with a pressure (e.g. a blade pressure) of between 1 and 1.5 bar. (II) Inks

The products made according to the present invention are suitable for use as pigments in aqueous inks and non-aqueous inks, including, for example, gravure inks, heat-set inks, lithographic printing inks, and newsprint inks. Depending on the final applications of the ink, the ink may further comprise at least one component chosen, for example, from resins, such as vinyl resins; polymers; additives, such as rheology modifiers, surfactants, and drying accelerating agents such as sodium lauryl sulfate, N,N-diethyl- m-toluamide, cyclohexylpyrrolidinone and butyl carbitol; fillers; diluents; humectants, such as ethylene glycol, propylene glycol, diethylene glycols, glycerine, dipropylene glycols, polyethylene glycols, polypropylene glycols, amides, ethers, carboxylic acids, esters, alcohols, organosulfides, organosulfoxides, sulfones, alcohol derivatives, carbitol, butyl carbitol, cellosolve, ether derivatives, amino alcohols, and ketones; and biocides, such as benzoates, sorbates, and isothiazolones. The ink product can further comprise at least one additional pigment chosen from those conventionally used in the art. The amount of products made according to the present invention in a given ink can vary greatly, based on the formulation of the ink, as would be apparent to one of ordinary skill in the art. For example, the products made according to the present invention can comprise from 5%-45% by weight of the ink as formulated.

(III) Rubber products

The products made according to the present invention may be incorporated into a rubber composition. The products may, for example, be used as fillers or extenders in the rubber composition. The composition comprising the products prepared according to the present invention can provide the benefits of resin extension, reinforcement and increased hardness of the rubber composition. The rubber product disclosed herein comprises at least one rubber chosen from natural rubbers and synthetic rubbers. For example, sulphur-vulcanisable rubbers, which can be used for the manufacture of tyre treads. Examples of the synthetic rubbers, which may be used in the present invention, include, but are not limited to, styrene-butadiene rubber (SBR), vinyl-styrene-butadiene rubber (VSBR), butadiene rubber (BR), and neoprene rubber or polyisoprene. The SBR may be emulsion SBR (E-SBR) or solution SBR (S-SBR). The VSBR may be solution VSBR (S-VSBR). Examples of the BR include, cis-1 ,3-polybutadiene rubber and cis-1 ,4-polybutadiene rubber. An example of the natural rubbers, which the products of the present invention can be used in is Standard Malaysian natural rubber. The rubber products may further comprise at least one additive chosen from conventional additives used in the art, for example, extender oils and mineral and synthetic fillers. The rubber can include an amount of the products to about 35% by weight as formulated.

(IV) Paints

The products produced according to the present invention may be used in paints, such as an aqueous or non-aqueous industrial coating, architectural paint, matt paint, glossy paint, deco paint, or art paint, comprising, in an appropriate medium, the products of the present invention. The products disclosed herein can serve, for example, as a gloss control agent pigment in the paint. The products will generally be present in an amount less than the critical pigment volume. However, products made according to the present invention can also be present in higher pigment volume concentrations, such as for example in the range of 1 % to 80% by weight on a dry film basis. The paint will typically further comprise at least one component chosen from binders, such as polymeric binders, for example, water dispersible binders chosen, for example, from polyvinyl alcohol (PVA) and latex; and additives conventionally used in paints, chosen, for example, from surfactants, thickeners, biocides, defoamers, wetting agents, dispersants, and coalescents. The paint may comprise at least one additional pigment chosen, for example, from TiO₂ and calcium carbonate.

(V) Polymer products

The products may be incorporated in polymer products and are typically present at a concentration of up to 60% by weight of the polymer as compounded and up to 30% by weight of the final polymer article. In addition to their role as pigments, the products can be used both for resin extension (i.e., filling), TiO₂ extension, and reinforcement of the polymer. The polymer product comprises at least one polymer resin. The term resin means a polymeric material, either solid or liquid, prior to shaping into a plastic article. The at least one polymer resin is one which, on cooling (in the case of thermoplastic plastics) or curing (in the case of thermosetting plastics), can form a plastic material. The at least one polymer resin, can be chosen, for example, from polyolefin resins, polyamide resins, polyester resins, engineering polymers, allyl resins, thermoplastic resins, and thermoset resins. The products may be combined with a polymer resin to form a polymer composition from which a shaped article is subsequently formed. "Polymer resin" is the general term used in the plastics art to denote a polymeric material (solid or liquid) prior to shaping into a plastic article. In the case of thermoplastic polymers, the polymer resin is melted (or otherwise softened) prior to formation of an article usually, by a moulding process, and the polymer will not normally be subjected to any further chemical transformations. After formation of the shaped article, the polymer resin is cooled and allowed to harden. In the case of thermosetting polymers, the polymer resin is in a precursor state which, after shaping, is cured to obtain the final polymeric article. In the curing stage, chemical crosslinks are formed. The products of the present invention are suited for use with polymer resins which are thermoplastic in nature or to polymer resins in which the resin is thermosetting.

The polymer resin composition may be made by methods which are well known in the art generally in which the product and the polymer resin are mixed together in suitable ratios to form a blend (so-called "compounding"). In general, the polymer resin should be in a liquid form to enable the particles of the filler to be dispersed therein. Where the polymer resin is solid at ambient temperatures, therefore, the polymer resin will need to be melted before the compounding can be accomplished. In some embodiments, the product may be dry blended with particles of the polymer resin, dispersion of the particles in the resin then being accomplished when the melt is obtained prior to forming an article from the melt, for example in an extruder itself.

In embodiments of the invention, the polymer resin and the product and, if necessary, any other optional additives, may be formed into a suitable masterbatch by the use of a suitable compounder/mixer in a manner known per se, and may be pelletized, e.g. by the use of a single screw extruder or a twin-screw extruder which forms strands which may be cut or broken into pellets. The compounder may have a single inlet for introducing the filler and the polymer together. Alternatively, separate inlets may be provided for the filler and the polymer resin. Suitable compounders are available commercially, for example from Werner & Pfleiderer. Examples of suitable additives include pigments other than those according to the present invention, antioxidants, processing aids, light stabilisers and glass fibre.

The polymer resin compositions incorporating the products of the present invention can be processed to form, or to be incorporated in, articles of commerce in any suitable way. Such processing may include compression moulding, injection moulding, gas- assisted injection moulding, calendaring, vacuum forming, thermoforming, extrusion, blow moulding, drawing, spinning, film forming, laminating or any combination thereof. Any suitable apparatus may be used, as will be apparent to one of ordinary skill in this art.

The articles which may be formed from the polymer compositions are many and varied. Examples include films, engineering thermoplastics and PVC cables.

(Vl) Ceramics

The product made according to the present invention may be incorporated into ceramic forming compositions. Ceramic articles are generally formed from a wet high solids composition which comprises a blend of various particulate ingredients which includes kaolinitic clays, i.e. clays which contain the mineral kaolinite. Often, fluxing materials such as china stone, feldspar or nepheline syenite and at least one silica containing material such as quartz or flint are included in such compositions. For the production of bone china the composition will also contain a substantial proportion of ground calcined animal bone. The composition may also include minor proportions of other ingredients such as calcium carbonate, dolomite and talc. The proportions of the various ingredients used in the composition will vary according to the properties in the fired ceramic article. Prior to firing the ceramic forming composition it is shaped and dried. The ceramic forming composition will need to have sufficient plasticity to enable it to be shaped and it must also possess sufficient strength in its unfired or "green" state to permit a certain amount of handling without loss of its integrity and shape.

(VII) Barrier coatings

The various product(s) may be incorporated into barrier coating compositions which comprise a slurry comprising the products according to the present invention. Typically the solids content of the slurry ranges from about 45% to about 70% by wt. Barrier coatings are generally useful in imparting to paper, moisture resistance, moisture vapour resistance, and resistance to grease, oil, air and the like. The amount of binder in the barrier coating may be in the range of about 40% to 50% by wt.

Claims

1. An integrated process for treating an ore of a white inorganic mineral to produce a product having improved optical properties, said process comprising:

a) providing said ore of a white inorganic mineral and physically separating the ore into a brighter fraction and a darker fraction, said darker fraction comprising discolouring impurities; b) dry crushing and/or grinding the brighter fraction; c) dry crushing and/or grinding the darker fraction and preparing an aqueous slurry of the resulting crushed and/or ground darker fraction; d) beneficiating the darker fraction obtained in (c) to remove at least some of the discolouring impurities; e) optionally, dewatering the beneficiated darker fraction obtained in (d); f) optionally combining at least a portion of the beneficiated darker fraction obtained in (d) or the dewatered beneficiated darker fraction obtained in (e) with at least a portion of the dry ground brighter fraction obtained in (b) to form said product having improved optical properties.

2. An integrated process according to claim 1 , wherein the beneficiated darker fraction obtained in d) is dewatered.

3. An integrated process according to claim 1 or 2, wherein the portion of the beneficiated darker fraction obtained in (d) or the dewatered beneficiated darker fraction obtained in (e) are combined with at least a portion of the dry ground brighter fraction obtained in (b) to form said product having improved optical properties.

4. An integrated process according to claim 3, wherein the dewatered beneficiated darker fraction obtained in (e) is combined with at least a portion of the dry ground brighter fraction obtained in (b) to form said product having improved optical properties.

5. An integrated process according to any one of the previous claims wherein in c) the aqueous slurry of the crushed and/or ground fraction is wet ground.

6. An integrated process according to the previous claim, wherein the wet grinding is carried out with at least about 30wt% water present.

7. An integrated process according to the previous claim, wherein the wet grinding is carried out with about 50wt% water present.

8. An integrated process according to the previous claim, wherein the wet grinding is carried out with about 70wt% water present.

9. An integrated process according to the previous claim, wherein grinding is carried out in the presence of one or more dispersants.

10. An integrated process according to any one of the previous claims, wherein the ore of the white inorganic mineral comprises, or consists of, or consists essentially of, calcium carbonate.

11. An integrated process according to the previous claim, wherein the ore of the white inorganic mineral is selected from one or more of marble, limestone or chalk.

12. An integrated process according to any one of the previous claims, wherein the wet ground darker fraction has a particle size distribution such that about 30wt% of the particles are less than about 2μm.

13. An integrated process according to any one of the previous claims, wherein the separation in a) is automated and comprises the use of one or more sensors.

14. An integrated process according to the previous claim, wherein the separation is carried out using one or more fluid streams.

15. An integrated process according to the previous claim, wherein the one or more fluid streams comprise a gas and/or a liquid.

16. An integrated process according to any one of claims 13 to 15, wherein the one or more sensors comprise at least one of a colour sensor or a reflectivity sensor.

17. An integrated process according to any one of claims 13 to 16, wherein the separating system is arranged so that the darker fraction substantially comprises particles possessing a brightness of < 95 ISO when the material is ground to substantially 90wt% finer than 2μm.

18. An integrated process according to the previous claim, wherein the brightness is < 92 ISO.

19. An integrated process according to any one of the previous claims, wherein beneficiation comprises one or more of froth flotation, magnetic separation, bleaching, leaching, electrostatic sorting.

20. An integrated process according to any one of the previous claims wherein following dewatering the solids content is about 60wt% to about 80wt%.

21. An integrated process according to any one of the previous claims wherein the products from one or more of b), d), e) and/or f) are optionally split and transported to a plurality of locations proximate to end users for additional processing to produce final products.

22. An integrated process according to any one of the previous claims, comprising the further steps of further processing the products obtained in one or more of b), d), e) and/or f) to form a final product selected from one or more of paper products, including fillers and coating formulations, inks, rubber products, paint compositions, polymer products, ceramics, barrier coatings.

23. An integrated process according to the previous claim, wherein the polymer products are formed into an article.

24. An integrated process according to any one of the previous claims, wherein combination of the fractions in f) is carried out in a granulator or the fractions are forced through a die to form a pellet of substantially uniform moisture.

25. An integrated system, suitable for carrying out the process according to any one of the previous claims, comprising

I. a device, e.g. an optical sorter, for physically separating the ore into a brighter

(and/or whiter) fraction and darker (and/or less white) fraction; II. a crusher and/or grinder for comminuting the brighter (and/or whiter) fraction; 111. a crusher and/or grinder, for comminuting the darker fraction;

IV. a source of water for preparing an aqueous slurry of the comminuted darker fraction; V. means for treating the aqueous slurry of the ground darker fraction; Vl. optionally, a dewatering device for dewatering the beneficiated darker fraction; VII. optionally, means for combining at least a portion of the treated fractions.

26. A system according to the previous claim, wherein the system further comprises a grinder for wet grinding the aqueous slurry in IV.