FIELD OF THE INVENTION

THIS INVENTION relates aggregation of small particles. The invention provides a binder composition. The invention also provides a method of agglomerating small particles using the binder composition. BACKGROUND TO THE INVENTION

RECOVERY OF SMALL PARTICLES, particularly those of 3mm and smaller and more particularly those of 750 micron and smaller, from bodies of material including such small particles, e.g. slimes dams and mine waste heaps, is often marginal because of shortcomings in the recovery methods that are used to. In the case of upsizing by agglomeration, which usually involves the use of liquids, high moisture levels in slurries containing the small particles often prevents processing the slurry and makes subsequent drying extremely difficult. Low resistance to attrition, the quantity of binder that is required and cost are also factors to bear in mind. Very frequently, the small particles that would be recovered have potential calorific value, may include valuable metals, may provide good fibres, and may have other valuable attributes. The small particles could also be hazardous. Examples are coal slimes, mineral slimes, high moisture filter cake such as paper mill sludge, fly ash, bag house fines and many more. In terms of hazardous fines, reference is made specifically to siliceous fines which are dangerous to inhale when smaller than 15 microns in size. Furthermore, small particles blown in the wind can settle on agricultural crops, interfering with photosynthesis or pollination or both.

The Applicant has, in the above context, identified a need for small particles agglomeration at lower cost and involving more practical aggregation chemistry.

SUMMARY OF THE INVENTION

IN THIS SPECIFICATION, "small particles" means particles having a mean particle size of 3mm or less, more preferably 750 micron or less and can include small particles that are dry and small particles that are wet, e.g. in the form of an aqueous suspension such as a slurry, or in the form of a sludge.

Furthermore, in this specification, "dry mass" means the mass of the concerned substance as measured on a dry basis for that substance. For example, an aqueous solution of polyvinyl alcohol that comprises 10% dry mass polyvinyl alcohol, comprises 10g of dry polyvinyl alcohol per 100g of solution. IN ACCORDANCE WITH ONE ASPECT OF THE INVENTION IS PROVIDED a binder composition for agglomerating small particles, the binder composition comprising a first aqueous solution, which comprises a fully or partially hydrolysed aqueous polyvinyl alcohol in a proportion of from 0.5% to 10% dry mass; and

a second aqueous solution, which comprises one or a combination of guar and galactomannan in a proportion of from 0.1 to 3% dry mass. The composition may, in particular, be a mixture of the first and second solutions. In some, less typical but nevertheless envisaged, embodiments, the composition may, however, comprise the first and second solutions separately, in which case the invention includes a method which includes separate application of the first and second solutions to small particles, thereby to form the composition as a mixture with the small particles. The small particles may, in particular, be a bulk mass, volume or bed of small particles. The binder composition may comprise up to 95 parts of the first aqueous solution and at least 5 parts of the second aqueous solution.

The binder composition may, more particularly, comprise up to 30 parts of the first aqueous solution and at least 70 parts of the second aqueous solution.

The first solution may, more preferably, comprise the polyvinyl alcohol in a proportion of from 0.5, more preferably 1.5 to 7.5% dry mass

A preferred form of polyvinyl alcohol is a fully hydrolysed polyvinyl alcohol in the molecular weight range of 100 000 to 175 000 and a degree of hydrolysis exceeding 98.5%, preferably exceeding 99%,

The second solution may, more preferably, comprise the guar and/or the galactomannan in a proportion of from 0.2 to 0.4% dry mass. The guar may, in particular, be guar gum. In one embodiment of the invention, the second solution may comprise from 0.25 to 2% guar and/or galactomannan dry mass. The first solution may then comprise polyvinyl alcohol in a proportion of 1 .25% dry mass. In such an embodiment of the invention, the binder composition may be useful specifically for dust suppression.

The guar and/or galactomannan may be linear polysaccharides. The guar and/or galactomannan may have a viscosity in the range of 2000 to 8000 cPas at a concentration of 1 % by mass in water.

Possible substitutes for or additions to guar and/or galactomannan include any one or a combination of any two or more of, optionally in combination with one or both of guar and galactomannan, locust bean gum, gum arabic, gum Karanya, xantham gum, Carrageanan, and gum tragacanth, all preferably as hydrated polysaccharides. It is noted that in the case of a combination the quantifications given apply to the combination and not to the components of the combination severally.

The binder composition may include a gelling, or crosslinking, agent. Preferably, the gelling agent is one that gels polyvinyl alcohol and guar and/or galactomannan. The gelling agent may be selected from any one or a combination of any two or more of a boron compound, specifically borax, as a solution in water, complexing compounds of any of the elements in groups IV to VI of the periodic table, manganese, titanium IV, zirconium IV, aluminium III, titanium V, calcium salts such as hydrated lime, potassium salts, sodium salts, aluminium salts, zinc salts, potassium phosphates, and sodium and potassium permanganate. The gelling agent may be provided as an aqueous gelling agent composition, comprising the gelling agent at a concentration of from 0.5% to 8% dry mass, more preferably 1 % to 6% dry mass. The gelling agent may be present in the binder composition in a range of 2 to 15 parts of the aqueous gelling agent composition per 100 parts of the binder composition without the aqueous gelling agent composition.

The aqueous gelling agent composition may include an auxiliary binder. The auxiliary binder may comprise an organic substance, more specifically any one or any combination of any two or more of:

organic compounds, such as polyvinyl acetates, polyvinyl alcohols both fully and/or partially hydrolysed;

thermoplastic emulsions based on acrylates, such as methyl methacrylates and methacrylic acid;

vinyl esters;

isocyanates with hydrolysed acrylics with hydroxyl numbers in the range 15 to

60;

furfural alcohols or furan precursors;

celluloses, such as sodium carboxymethyl cellulose or hydroxyl propyl or hydroxyl ethyl cellulose, or co-polymer celluloses;

natural binders, such as polysaccharides, gums, collagen, gluten, gelatine, caseins, starches, and dextrins;

phenolic compounds and resins, optionally pre-dissolved in methanol;

styrenated emulsions, such as acrylates; bitumen emulsions;

lignosulphonates,

water miscible isocyanates or epoxies;

wattle or acacia extracts; and

tree resins.

Alternatively, or additionally, the auxiliary binder may comprise an inorganic substance, on its own or modified by organic compounds or mixtures of inorganic binders as solutions in water, more specifically any one or any combination of any two or more of:

sodium or potassium silicates;

phosphates or chloride precursor solutions for caustic magnesium;

sodium carbonates or hydroxides or potassium carbonates or hydroxides as precursors for geopolymers, or alternatively as small dry particles such as flyash, particularly those high in reactive oxides of silica, iron and aluminium;

Portland cement;

high alumina cement;

gypsum;

caustic magnesium; and

calcium hydroxides or hydrated lime acting either as geopolymer precursors or as hydraulic binders.

The binder composition may also include fibrous material. More specifically, the binder composition may include fibres from 2mm to 15mm in length, more preferably 3mm to 12mm in length. The fibres may be selected from any one or a combination of any two or more of

organic synthetic fibres, including polypropylene, acrylic, polyvinyl alcohols, nylons, polyethylene tetraphthalates, and polyesters;

carbon; and

inorganic fibres, including glass, ceramics, steel or other metals, wollastonite, ettringite, platelets including mica, vermiculites, and clays including bentonites.

The binder composition may also include a foam. The foam may be a partially hydrolysed polyvinyl alcohol foam, generated from an aqueous solution of a partially hydrolysed polyvinyl alcohol, for example Mowiol 18/88 by Clariant or Poval 217 by Kururay. The concentration of the partially hydrolysed polyvinyl alcohol in the aqueous solution of the partially hydrolysed polyvinyl alcohol may be as low as 0.5%, but more preferably 1 .5%, and even more preferably between 2.5 and 7.5% dry mass, and most preferably 3.5% to 6% dry mass. In such a case, the binder composition would typically not include the gelling agent.

In one embodiment of the invention, the foam may be the first aqueous solution. In some embodiments, particularly when the binder composition includes the gelling agent, the binder composition may be in a gelled form. In such a form, the binder composition may be continuous, or may be in particulate form. The binder composition may also include small particles, as described below in relation to the method of the invention. This is particularly applicable when the binder composition is in a gelled form. IN ACCORDANCE WITH ANOTHER ASPECT OF THE INVENTION IS PROVIDED a method of agglomerating small particles, the method including

forming a mixture of the small particles and a binder composition that comprises a first aqueous solution, which comprises a fully or partially hydrolysed aqueous polyvinyl alcohol in a proportion of from 0.5% to 10% dry mass; and a second aqueous solution, which comprises one or a combination of guar and galactomannan in a proportion of from 0.1 to 3% dry mass, and allowing or causing the binder composition to gel the mixture, thus enveloping the small particles within a gelled binder composition. The mixture may be formed by first forming a mixture of the first and second aqueous solutions, as the binder composition, and then forming a mixture of the binder composition and the small particles. Alternatively, the mixture may be formed by pre- mixing one of the first and second aqueous solutions with the small particles, and then mixing the other of the first and second aqueous solutions with the pre-mixture.

The term "forming a mixture", "mixing", etc. when used in relation to the small particles is regarded as including contacting a continuous or non-continuous bed of small particles with the binder composition, in situ. Such contacting would therefore not need to include a mixing operation, but can involve merely applying the binder composition to the small particles, e.g. by means of spraying. This also applies to the aqueous gelling agent composition when not included as part of the binder composition.

The mixture may be in the form of a suspension, e.g. a slurry, or a sludge.

The mixture of the small particles and the binder composition may comprise the binder composition in an amount of from 2 to 35%, more preferably from 5 to 20% based on the weight of the small particles without the binder composition. In this regard in particular, it must be borne in mind that the small particles may be dry or may be wet. The specific amount of the binder composition that is used would depend on the wetness of the small particles, e.g. the concentration of small particles in the slurry or sludge.

When the binder composition does not include a gelling agent, causing the binder composition to gel the mixture may include mixing a gelling agent, for the binder composition or for one or both of the aqueous solutions thereof, with the small particles or with the mixture.

The gelling agent may be a gelling agent that gels polyvinyl alcohol and guar and/or galactomannan. The gelling agent may be selected from any one or a combination of any two or more of a boron compound, specifically borax, as a solution in water, complexing compounds of any of the elements in groups IV to VI of the periodic table, manganese, titanium IV, zirconium IV, aluminium III, titanium V, calcium salts such as hydrated lime, potassium salts, sodium salts, aluminium salts, zinc salts, potassium phosphates, and sodium and potassium permanganate. The gelling agent may be provided as an aqueous gelling agent composition, comprising the gelling agent at a concentration of from 0.5% to 8% by mass, more preferably 1 % to 6% by mass. The gelling agent may be added in a range of from 2 to 15 parts of the aqueous gelling agent composition per 100 parts of the binder composition without the aqueous gelling agent composition.

The binder composition may gel the mixture by becoming gelled, or cross-linked, itself, at from 0.001 to 0.5%, more preferably at 0.01 % to 0.25% on a dry mass basis.

The gelling agent is not necessary in all embodiments, and the method may include allowing the binder composition to gel by desiccation of the binder composition, also to obtain a gelled binder composition in accordance with the method of the invention. It must further be noted that in some embodiments of the invention, the binder composition may include the gelling agent, in which case the binder composition may be pre-gelled when mixed with the small particles. This is presented as a separate aspect of the invention, involving pre-gelling of the binder composition and subsequent mixing with the small particles. In such a pre-gelled form, the binder composition itself may be in particulate form, having formed as such due to gelling or having been formed as such by mechanical breaking. In such a case, the further processing referred to below to form the particles into artefacts may be carried out on a mixture of pre-gelled binder composition particles and the small particles. This is particularly relevant to pressing. In such an embodiment, when the binder composition is a gelled binder composition, the method may still include forming a mixture of the gelled binder composition and the small particles, and causing the binder composition to gel the mixture may include subjecting the mixture to further processing as described below in order to form the mixture into artefacts, e.g. by pressing. In another embodiment, the gelled binder composition comprising the small particles may be mixed with further small particles and the mixture then subjected to further processing as described below in order to form the mixture into artefacts. In such a pre-gelled form, the binder composition itself, enveloping the small particles, may be in particulate form, having formed as such due to gelling or having been formed as such by mechanical breaking.

The small particles may be any one or a combination of any two or more of

dry or wet mineral fines;

dry or wet biomass, typically to produce board products and optionally additionally bound by any one or a combination of any two or more of alkali metal silicates, a phenol formaldehyde resole resin with a sulphonic acid catalyst cured at room temperature, and an isocyanate;

lignocellulose fibres, typically to produce board products and optionally additionally bound by any one or a combination of any two or more of alkali metal silicates, a phenol formaldehyde resole resin with a sulphonic acid catalyst cured at room temperature, and an isocyanate;

sludges, particularly ultra wet sludges for recovery by cascade drying the granulates e.g. paper mill sludge, paper mill black liquor and carbonaceous sludge; particulate material prone to generate dust; e.g. loose particles on unpaved road surfaces or any other surface, specifically ground surface, from which such particles may be rendered airborne;

fertilizer;

waste materials such as milled waste carpets, mono-filament glass, rockwool, cellulose acetate fibres, milled super absorbent impregnated fabrics, and textile fibres; shredded or sheet stock of open cell flexible foam, such as plasticised polyvinyl chloride, polyurethane foams impregnated and then wet compressed for excess removal for the production of rigid light weight cellular boards or formed shape items; and

milled grain, specifically damp milled grain for animal or human food, requiring to be granulated and dried, facilitating handling and transportation, preferably using a calcium salt solution such as hydrated lime as aqueous gelling agent composition.

The method may include adding to any one or a combination of two or more of the binder composition, the small particles, the mixture and, more preferably, the aqueous gelling agent composition, a potassium methyl siliconate. The potassium methyl siliconate may be added in an amount from 0.25 to 0.5% dry mass based on the weight of the binder composition without the potassium methyl siliconate. The potassium methyl siliconate may impart hydrophobicity and thus water resistance to the gelled binder composition, specifically once it is exposed to and reacts with atmospheric carbon dioxide. BS-16 by Wacker is a particularly suitable siliconate.

The method may also include providing a foam as part of the mixture of the binder composition and the small particles, when the binder composition itself does not include a foam. The foam may be a partially hydrolysed polyvinyl alcohol foam, generated from an aqueous solution of a partially hydrolysed polyvinyl alcohol, for example Mowiol 18/88 by Clariant or Poval 217 by Kururay. The concentration of the partially hydrolysed polyvinyl alcohol in the aqueous solution of the partially hydrolysed polyvinyl alcohol may be as low as 0.5%, but more preferably 1 .5%, and even more preferably between 2.5 and 7.5% dry mass, and most preferably 3.5% to 6% dry mass. Causing or allowing the mixture to gel may then occur after the foam has been provided as part of the mixture of the binder composition and the small particles. Gelling of the mixture in forming the gelled binder composition enveloping the small particles may result in the gelled binder composition forming as a particle bed, comprising discrete non-sticky particles, each particle comprising gelled binder composition enveloping part of the small particles. This is not expected in the case in which a foam is included in the mixture of the binder composition and the small particles.

When the gelled binder composition is, instead, a continuous mass, the method may include mechanically breaking the gelled binder composition into solid particles of random shapes or predetermined shapes, each particle comprising gelled binder composition enveloping part of the small particles.

The method may include forming the particles, whether resulting from gelling or obtained by mechanical breaking, into artefacts by any one or a combination of any two or more of the following forms of processing:

rolling, to form granules; pressing;

briquetting;

extrusion; and

block making.

When the gelled binder composition forms as a particle bed, comprising discrete non- sticky particles, each particle comprising gelled binder composition enveloping part of the small particles, or when the binder composition is pre-gelled into particles and provided as a mixture with the small particles, or when particles of the gelled binder composition enveloping the small particles is provided as a mixture mixed with further small particles, excess water contained in the particles and having been enveloped by the particles upon gelling may be dispensed from the particles due to forming the particles into artefacts, specifically in the case of pressing, by syneresis, with gel stability being assured by heteresis. These phenomena may be affected by temperature influences on the gel.

DETAILED DESCRIPTION OF THE INVENTION

THE INVENTION WILL NOW BE DESCRIBED IN MORE DETAIL by way of illustrative example only, with reference to the accompanying drawings which show, diagrammatically, processes for implementing a method according to the invention in relation to various feedstocks of small particles, some of which are specifically exemplified hereinafter.

Referring to the drawings and specifically to Figure 1 , reference numeral 10 generally indicates a process for implementing a method according to the invention. The process 10 represents various possibilities for implementing the method, which are described in more detail below. Broadly, the process 10 includes respective small particle feedstocks comprising, respectively, mineral fines 12, biomass fibre 18, ultra wet sludge 20, fertilizer material 22, which could also be lime, gypsum or fly ash, and damp milled hominy chop or grain 24. These small particle feedstocks are not treated in the process 10 simultaneously, and are presented on the same drawing merely for convenience. All of these are small particle feedstocks as for the agglomeration of which the present invention provides.

The process 10 further includes an aqueous polyvinyl alcohol solution feedstock 14, comprising an aqueous polyvinyl alcohol solution as a first aqueous solution of the binder composition in accordance with the invention.

The process 10 also includes an extender feedstock 16.

The process 10 is configured for the feedstocks 12, 18, 20, 22, and 24 to be delivered, respectively, to a mixer 30.

The process is also configured for at least the aqueous polyvinyl alcohol solution 14, but preferably also for the extender 16, to be delivered to the mixer 30, typically separately of the feedstocks 12, 18, 20, 22, and 24. The process 10 further includes an aqueous gelling agent composition feedstock 28, comprising an aqueous gelling agent composition in accordance with the invention. The process 10 is configured for the feedstock 28 to be delivered to the mixer 30, typically separately of the feedstocks 12, 14, 16, 18, 20, 22, and 24.

The process 10 also includes an aqueous solution of guar and/or galactomannan feedstock 34 as a second solution of the binder composition in accordance with the invention. The process 10 is configured for the feedstock 34 to be delivered to the mixer 30, typically separately of the feedstocks 12, 14, 16, 18, 20, 22, 24, 28.

It must be noted that while the process 10 is configured for separate delivery of the feedstocks 12, 18, 20, 22, and 24, respectively, the feedstock 14, the feedstock 16, the feedstock 28 and the feedstock 34 to the mixer 30, these feedstocks may be fed to the mixer simultaneously, and in any event in a manner that results in the feedstocks 12, 18, 20, 22, and 24, respectively, being inside the mixer 30 at the same time as the feedstock 14, optionally the feedstock 16, the feedstock 28 and the feedstock 34.

For the purpose of producing cement and gypsum fibre boards and particle boards at room temperature, e.g. mineral boards, the process 10 includes, following the mixer 30, a spreader 40, a daylight press or double press 44, a curing stage 50, a sanding stage 54 and a sawing/dimensioning stage 56.

For the purpose of granulating ultra wet sludges, the process 10 includes, following the mixer 30, a rotary granule shaping roller 42 and a rotary cascade dryer 46. For the purpose of forming briquettes, extrudates and/or blocks, the process 10 includes, following the mixer, the rotary granule shaping roller 42, a briquetting, extruding or block pressing stage 48 and a dryer 52. In Figure 1 , discharge from the mixer 30 is a gelled binder composition as obtained in accordance with the method of the invention.

Referring to Figure 2, which shows another embodiment of the process 10, specifically for dust suppression, the process 10 includes the feedstocks 14, 28 and 34 and the mixer 30, to which the feedstocks 14, 28 and 34 can be delivered in the same manner as described in relation to Figure 1 . Discharge line 59 represents discharge of the product from the mixer 30 onto a surface that comprises particles that are prone to becoming airborne and forming airborne dust. In Figure 2, feedstock 28 can either be delivered to the mixer 30 along line 58, in which the case the product from the mixer 30 along discharge line 59 will include the feedstock 30, or can be delivered directly to the surface that comprises particles that are prone to becoming airborne and forming airborne dust, as represented by discharge line 60. In such a case, the product from the mixer 30 would be a binder composition in accordance with the invention. In use, the process may include discharging the binder composition, optionally with an auxiliary dust suppressant, onto the surface, followed by discharging the feedstock 28, i.e. the aqueous gelling agent composition, onto the surface. It is noted that while the feedstock 28 is preferred and would be present and used in most embodiments of the invention, there are embodiments of the invention in which it is not necessary, specifically when the binder composition of the invention, and any small particles that it may contain, would be allowed to gel by desiccation.

In one embodiment of the invention in use, referring to Figure 1 , the feedstocks 14 and 34 are delivered to the mixer 30 and mixed, thereby forming a binder composition in accordance with the invention. Thereafter, one of the feedstocks 12, 18, 20, 22, and 24 would be delivered to the mixer 30 and mixed with the binder composition. Thereafter, the feedstock 28 would be delivered to the mixer 30, would react with the binder composition and gel, or cross-link, it, thereby producing a gelled binder composition that envelops the feedstock 12, 18, 20, 22, or 24. The gelled binder composition would then be processed as described above. In another embodiment of the invention in use, still referring to Figure 1 , the feedstocks 14, 34 and 28 are delivered to the mixer 30 and mixed, thereby forming a gelled binder composition that does not envelop any small particles, and then delivering to the mixer 30 one of the feedstocks 12, 18, 20, 22, and 24, thereby obtaining a mixture of the feedstock 12, 18, 20, 22, or 24 and the gelled binder composition. The mixture would then be processed further as described above. Such processing may then result in small particles of one of the feedstocks 12, 18, 20, 22, and 24 becoming enveloped by the gelled binder composition. This embodiment is presented as an independent aspect of the invention. In a further embodiment of the invention in use, still referring to Figure 1 , one of the feedstocks 12, 18, 20, 22, and 24 and the feedstock 28 are delivered to the mixer 30 ad mixed. Then, the feedstocks 14 and 34 are delivered to the mixer 30 and mixed with the mixture of one of the feedstocks 12, 18, 20, 22, and 24 and the feedstock 28. Delivering the feedstocks 14 and 34 to the mixture of one of the feedstocks 12, 18, 20, 22, and 24 and the feedstock 28 effectively provides the binder composition of the invention in mixture with the one of the feedstocks 12, 18, 20, 22, and 24 and the feedstock 28. Thus, the feedstock 28 reacts with the feedstocks 14 and 34, i.e. the binder composition, causing it to gel in the presence of the small particles, i.e. one of the feedstocks 12, 18, 20, 22, and 24, and thus forming a gelled binder composition enveloping small particles in accordance with the invention. The gelled binder composition would then be processed as described above.

In still a further embodiment of the invention in use, referring now to Figure 2, the process 10 includes delivering the feedstocks 14 and 34 to the mixer 30 and mixing them, thereby obtaining a binder composition according to the invention that excludes a gelling agent, and delivering the binder composition thus obtained to a surface that comprises particles that are prone to becoming airborne and forming airborne dust, and allowing the binder composition to gel by desiccation.

In yet a further embodiment of the invention in use, still referring to Figure 2, the process 10 includes delivering the feedstocks 14, 28 and 34 to the mixer 30, thereby obtaining a binder composition according to the invention that includes a gelling agent, and delivering the binder composition thus obtained to a surface that comprises particles that are prone to becoming airborne and forming airborne dust, and allowing the binder composition to gel by reaction with the gelling agent.

In still a further embodiment of the invention in use, still referring to Figure 2, the process 10 includes delivering the feedstocks 14 and 34 to the mixer 30 and mixing them, thereby obtaining a binder composition according to the invention that excludes a gelling agent, and delivering the binder composition thus obtained to a surface that comprises particles that are prone to becoming airborne and forming airborne dust. Thereafter, the feedstock 28 is delivered to the surface, causing gelling of the binder composition by reaction with the gelling agent.

Although not illustrated, the process 10 may include a polyvinyl alcohol foam- generating stage, in which an aqueous solution of a partially hydrolysed polyvinyl alcohol, such as Mowiol 18/88 by Clariant or Poval 217 by Kururay, at a concentration in the partially hydrolysed polyvinyl alcohol aqueous solution of as low as 0.5%, but more preferably 1 .5%, and even more preferably between 2.5 and 7.5% dry mass, and most preferably 3.5% to 6% dry mass is pumped at constant pressure and volume and into which is injected compressed air, with the appropriate non-return valves, into a tube coiled in several coils. The solution inverts several times in the moving air stream in the coils to produce an air saturated light, very low density foam of from 15 to 60 grams per litre. Such a stage may deliver the foam to the mixer 30 prior to introducing the aqueous gelling agent composition feedstock 28 into the mixer 30, to be mixed with the feedstock 12, 18, 20, 22, or 24, the feedstock 14 and the feedstock 34 in the mixer, such that when the feedstock 28 is introduced into the mixer 30, the foam is gelled as well. EXAMPLES

Mineral Building boards

Gypsum hemi-dydrate, an alkali metal silicate dry powder or calcium aluminate, bound by Portland cement, is converted to a paste or slurry, with a binder composition in accordance with the invention, comprising a first solution of guar in water, at a dry mass of guar of 0.5 to 2.5% of the solution, and a second solution of polyvinyl alcohol, preferably a fully hydrolysed polyvinyl alcohol, in water, at a dry mass of the solutions being present in the binder composition in a mass ratio of ... .

After thorough mixing, an aqueous gelling agent composition in accordance with the invention, preferably a 3% to 8% dry mass solution of borax in water, is added at 5% to 15% dry mass based on the mass of the binder composition.

As the mixture of the binder composition, the small particles and the aqueous gelling agent composition is mixed, the binder composition gels the mixture, enveloping the small particles, and automatically converts to quite small, 3mm to 8mm granules which are non-sticky, free flowing and spreadable.

The granules thus obtained are subsequently fed to a press, spread to the requisite mass per unit area, and pressed at room temperature for 4 to 15 seconds at a pressure of 5 to 30kgs per square centimetre. The granules coalesce to form a uniform consistent cohesive artefact, in the form of a board, preferably on a platen, ready for curing or drying as the case may be. Inclusion of the polyvinyl alcohol solution improves the water resistance of the artefact.

Particular advantages include that the water added may be controlled to that amount required for hydration of the hydraulic binder. Also, the process is very fast, density is controlled by lightweight particle addition, such as expanded perlite or exfoliated vermiculite, and fibre reinforcement can be mixed with the slurry.

Pressing may be at thicknesses from 4mm to 75mm or more, at final densities in the range 0.7 to 1.7 grams/cc and reinforcing steel bar or mesh, or acrylic coated glass fibre crinette, or electric conduit or water pipe may all be pressed integral with the composite as required.

Light weight building blocks comprising 30mm cement board, at a cured density of 1 .10 grams/cc, may be laminated either side of a polymeric foam, such as expanded polystyrene foam or Neopor by BASF. A typical compressive strength is 7 m Pa or greater at a bulk density of the composite of 0.96, making logistics and construction fast and logistically efficient. Cement or Gypsum Foams

A slurry of a binder composition according to the invention comprising a first solution containing 0.5 to 2.0% dry mass guar gum in solution and a second solution containing 0.5 to 5.0% dry mass of a polyvinyl alcohol, preferably fully hydrolysed, is formed with small particles comprising either or both of gypsum or cement. A very fine or small air cell foam is generated by an aqueous solution of a partially hydrolysed polyvinyl alcohol, such as Mowiol 18/88 by Clariant or Poval 217 by Kururay, at a concentration in the partially hydrolysed polyvinyl alcohol aqueous solution of as low as 0.5%, but more preferably 1.5%, and even more preferably between 2.5 and 7.5% dry mass, and most preferably 3.5% to 6% dry mass that is pumped at constant pressure and volume and into which is injected compressed air, with the appropriate non-return valves, into a tube coiled in several coils. The solution inverts several times in the moving air stream in the coils to produce an air saturated light, very low density foam of from 15 to 60 grams per litre. Surplus air is allowed to escape at a foam delivery point where the foam is delivered to the slurry.

The foam is delivered to and blended with the slurry, preferably in an anti-gravity contra rotating double shaft paddle mixer, in which the added foam is enveloped and gently blended with the slurry.

The foamed cement or gypsum is subsequently "frozen" or gelled by adding an aqueous gelling agent composition, such as a borax solution of 3 to 8% dry mass borax in water to the foamed slurry at 5 to 15 parts of the borax solution by mass of the foamed slurry.

A three dimensional polyvalent metal crosslink is formed, having a gel strength of 500 to 2000 grams pressure per square centimetre. The foam can now be cut or profiled or surface patterned, preferably while wet, and then dried as boards, sheets, insulation profiles, door cores and fire protection panels. The starting slurry may have blended into it milled carpets or textiles, or monofilament glass or rockwool. Fibrous Composites

A binder composition according to the invention comprising a first solution that is an aqueous guar solution containing guar in a dry mass concentration in water from 0.5 to 3.0%, more preferably between 0.5 and 2.0%, and a second solution of polyvinyl alcohol, preferably a fully hydrolysed polyvinyl alcohol, in water, at a dry mass of the solutions being present in the binder composition in a mass ratio of... and the binder composition being un-gelled or crosslinked, is used to wet a fibrous feedstock chosen from milled carpets, textiles, monofilament glass or rockwool or lignocellulosic fibre.

Once the fibres are covered by the binder composition, an auxiliary binder is added, chosen from cement or gypsum in dry powder form, the water for hydration being provided by the binder composition.

The fibrous feedstock with the auxiliary binder is pressed at room temperature to form a flat or profiled composite.

In another aspect, a phenol formaldehyde resole resin, pre-catalysed with a sulphonic acid, or an isocyanate, or a blend between them is added with suitable mixing. The reaction proceeds at room temperature, the isocynate reacting with water or with the phenolic resin, or the phenolic resin reacts with the acid. The composite is pressed at ambient temperature and the reaction proceeds further after the cohesive composition has been formed. In this regard the guar acts substantially as a process aid, although a reaction between hydroxyl groups and the acid assists. The isocyanate reaction can be rapid at room temperature.

DISCUSSION

Polyvinyl alcohol

The method and binder composition of the invention include preparation of a solution of polyvinyl alcohol in water, in which the polyvinyl alcohol is rapidly soluble only at elevated temperatures, preferably above 90°C, in order to create molecular separation in the water. The preferred polymer is a fully hydrolysed polyvinyl alcohol in the molecular weight range 100000 to 175000, a degree of hydrolysis exceeding 98.5% preferably exceeding 99%, and used at a concentration by dry weight in water for the purpose of the invention at from 0.5% - 10%, more preferably from 1.5% - 7.5%.

Polyvinyl alcohol as a binder has a number of unique properties some of which are of the following, and relate to the polyvinyl alcohol of the aqueous polyvinyl alcohol solution of the binder composition of the invention:

- Polyvinyl alcohol is an excellent binder with good adhesive and film strength.

- Polyvinyl alcohol forms a film that has good tear strength as well as elongation at break. The partially hydrolysed grades have a higher elongation at break than the fully hydrolysed grades which are more rigid. This allows for choice depending on the application, such as resistance to shock.

- The film has high gas impermeability and resistance to organic solvents and yet still retains high moisture permeability. This is a unique benefit in the method of the invention where rapid drying is needed, and the aggregated material is desired to have a strong peripheral film. - The different grades of polyvinyl alcohol allow a wide spectrum of choice. For example the partially hydrolysed grades such as Mowiol 18/88, 23/88 and 26/88 by Clariant and G-types by Nippon Gohsei such as GH17 to GH22, have the property of low surface tension which can propagate intimate wetting.

- The polyvinyl alcohols have increasing tensile strength with increasing degree of polymerisation and molecular weight. The partially hydrolysed grades, at a given concentration in water, have a lower viscosity than the fully hydrolysed or saponified types. There is therefore an ideal molecular weight range at the acceptable concentration levels suitable for the invention. These are Mowiol grades 18/88, 23/88 and 26/88 by Clariant and the G-types GM14 and GH17 to GH22 by Nippon Gohsei and in the fully hydrolysed or saponified grades, Mowiol 20/98 by Clariant and the Gohsenol N-types NH18, NH20, NN14 and N300 by Nippon Gohsei with molecular weights in the range 100 000 to 160 000 and viscosities of a 4% solution at 20°C in the range 16 to 30mPa.s, with a degree of hydrolysis or saponification mol percent in the partially hydrolysed grades of between 86 and 88, an approximate ester value in mgKOH/g of 140 ± 10 in the partially hydrolysed grades and in the fully hydrolysed grades, a degree of hydrolysis or saponification mol percent between 97 and 99 and an ester value of 20 ± 5mgKOH/g.

- Solubility in water and rigidity increase with increasing saponification and molecular weight. The fully hydrolysed grades such as N300 by Gohsenol or 20/98 by Mowiol have a higher degree of water insolubility at room temperature and a higher capacity for gelation. These are preferred for composite binding.

- Increasing drying temperature improves resistance to water solubility in both types but water proofing agents may also be used such as Glyoxal, Dimethylol Urea, or acids such as orthophosphoric acid or certain salts such as ammonium chloride or sodium / ammonium bichromate, these typically being added at 5% by mass on the polyvinyl alcohol. Adding aldehydes are other options.

- The polyvinyl alcohols have a lesser susceptibility to putrefaction, decomposition or polymerisation than most other binders.

- Typical gelation agents are Borax or boric acid.

- Certain compounds can be used to inhibit gelation during storage or process until the required point in time. Examples are sorbic acid, rhodan salt or a higher alcohol.

- Preservatives to prevent attack by micro-organisms such as sodium dehydroacetate, potassium sorbate or sodium pentachlorophenol are effective at levels of 0.01 % to 0.4% by mass of the aqueous solution.

- Dissolution of polyvinyl alcohol is best done by dispersion at room temperature and then increasing the heat of the mixture to 90 to 95°C. Complete dissolution then takes place within 10 to 20 minutes. This is particularly important in the case of the fully hydrolysed or saponified grades. The formation of a polyvinyl alcohol solution in this manner is expressly cited as forming part of the invention, specifically in preparing the first aqueous solution of the binder composition.

- Gelation can be critical to final product quality, imposing cohesion, improved binding, reduced stickiness in process and superior granulation, and subsequent green adhesion and cohesion of the wet granules when pressed, which after drying, result in a strong agglomerate. During pressing, excessive water enveloped by the gelled binder composition may be expelled without loss of the gelled binder, typically by syneresis. - Other synergistic binders may be used in conjunction with a polyvinyl alcohol. Examples, apart from synthetic resins, are hydrated polysaccharide hydrocolloids of natural origin. Considerations influencing the choice of the polyvinyl alcohol grade are the following:

- Molecular mass, degree of polymerisation and viscosity of an acceptable concentration in water. The possible molecular weight ranges are between 14,000 and 175,000 more preferably between 1 10,000 and 160,000 and degree of polymerisation of 270 to 3,000 that preferred in the region of 2,800. The maximum concentration in water is approximately 20% and the normal minimum would be 0.75%.

- The propensity to gel.

- The solubility at room temperature in water after drying. The fully hydrolysed or saponified grades may be superior in this respect.

- The drying temperature. The higher this is the greater the subsequent insolubility in water.

- The percentage concentration required and its behaviour both in use and in drying. Guar

Guar, specifically guar gum, is a linear polysaccharide, the viscosity of which is lower at low temperature. Upon gelling, a guar gel is stable up to 50°C. Guar is non-ionic and hydrocolloidal, and is not affected by ionic strength or PH. It has its greatest stability at a PH of 5 to 7. Guar has up to eight times the thickening propensity of corn starch but is strongly shear thinning. It is a strong emulsifier as a function of viscosity, which is highest at a dissolution temperature of 70°C. Viscosity of a 1 % solution is in the range 3500 to 8000 cPa's.

Guar or galactomanan is extracted from the ground endosperm of guar beans. Both contribute to a viscous solution in water and may be used together, both are natural polymers, both are binders and a guar solution at 0.5% to 2% or lower may be gelled with borax or calcium at room temperature.

The guar plant is similar to soya in appearance and is drought resistant. It is a leguminous shrub, cyanopsis tetragonoloba. Guar gum consists of 36.0% galactose anhydride and 63.1 % mannose anhydride referred to as galactomannan, of molecular weights 220,000 and is a linear anisodimensional carbohydrate polymer.

Guar is in fact a long chain polyalcohol with 1 - 2 diol groupings capable of complexation. It is non-ionic or cationic or anionic. It binds water through hydrogen bonding, as free hydroxyl groups, its film is resistant to oils and greases and it is stable across a wide range of Ph.

Guar with polyvinyl alcohol in ranges 60 parts guar to 40 parts polyvinyl alcohol is preferred in the invention, but for dust suppression a guar solution of 0.15% to 0.4%, more specifically 0.2% to 0.35% dry mass of a 5,000 cPas viscosity guar combined with 1.25% dry mass polyvinyl alcohol solution, can be effective. Wide combinations of different concentrations in water are possible. Guar with polyvinyl alcohol, complexed by Boron B(OH) ₄ - forms rigid three dimensional polyvalent metal crosslinks. Guar may be complexed on its own in the same way to granulate cement or gypsum or calcium aluminate slurries for boards, damp milled grains, fertilizer constituents, lignocellulosic fibres, for boards, coal fines, mineral fines, carpets, textiles or inorganic fibres for pressed products and others variously described above.

Guar of molecular weights of 100,000 to 3 million may be used at concentrations of 0.15% to 3% dry mass in water and be crosslinked at 0.001 % to 0.5%, more preferably between 0.01 % to 0.25%, examples of suitable gelling agents being sodium or potassium permanganate or the compounds or elements mentioned previously.

Typical guar crosslinks are depicted below. Crosslinking on gelation of the guar and polyvinyl alcohol blend may precede or succeed blending with the small particles or feedstock depending upon viscosity or gel rigidity and to ensure intimate particle wetting of the small particles and resistance to subsequent binder dissolution.

Ho

Ho

R R

Gelling of guar and polyvinyl alcohol The crux of the invention is the two-part binder composition, both parts being compatible with each other and both forming gels with a common gelling agent, which may be referred to as co-gelation or crosslinking. The gelling of the polyvinyl alcohol and guar is to cause the formation of discreet, non- sticky particles or granules which may be pressed to form a fibrous sheet by instant cohesion at room temperature. The Penguin Dictionary of Chemistry describes an association as a, 'term applied to the combination of molecules of one substance with those of another to form more complex molecules'. The Oxford Dictionary of Chemistry describes the phenomenon as, 'a combination of molecules of one substances with those of another to form a chemical species that are held together weaker than normal chemical bonds'. The Oxford Dictionary of Chemistry describes 'complexation' as, 'a compound in which the molecules or ions form co-ordinate bonds to a metal atom or ion'. The classic complex formed from polyvinyl alcohol is its reaction with boric acid or one of the borates. Boric acid gives a monodiol complex which in turn forms a polyelectrolyte, the 'didiol complex'. The gelation particularly suitable to the method of the invention is the precipitation or complexation or the formation of an association of the polyvinyl alcohol as well as the guar by borax in solution which is Na2B ₄ O5(OH) ₄ .8H2O referred to as disodium tetraborate decahydrate. Borax partially hydrolyses to boric acid and acts as a buffer. In the method of the invention borax is dissolved in water to give a solution concentration of 0.5% to 8% by mass, more preferably in the range 1 % to 6%. This solution, when blended to the polyvinyl alcohol solution and guar contained blend is used in the range 1 % to 15% of borax solution by mass on the mass of the polyvinyl alcohol / guar blend solution, more preferably in the range 7.5% to 12.5%. Other complex forming compounds are the elements of sub-groups 1 V to V1 of the periodic table, and some of the manganese compounds. This gelation results in a rigid three dimensional polyvalent metal crosslink. The gelation agent is specific to both the polyvinyl alcohol and the guar solutions in water, the resulting gel is not water soluble.

Alternatively uses for the binder composition of the invention, presented as separate aspects of the invention, include:

- to impregnate porous substrates such as a PU foam pieces, milled carpets, textile waste, inorganic monofilament fibre as a binder and process aid before pressing with or without gellation, with an auxiliary binder chosen from an alkali silicate solution set by acid precursors or calcium or with a phenol formaldehyde resole resin catalysed by sulphonic acid;

- gelling of small particles in situ in the substrates in which they occur, such as slimes dams or ash discard heaps to a depth of 25 to 75mm, either to provide a waterproof capping or as a means of breaking the gelled and dried fines into handle-able pieces for recovery or transportation, in which case the gelling agent can be present in the substrate;

a very dilute solution can be used as a dust suppressant by application to roads or other surfaces, which suppressant rapidly gels and holds the minute dust particles into aggregates, with or without an added binder, and guar is ideal at a 0.1 % to 0.3% concentration with a fully hydrolysed polyvinyl alcohol at 0.5% to 1 .5% concentration in the suppression solution (should the substrate not contain a gel agent, the fully hydrolysed polyvinyl alcohol binds the guar on dessication as a water insoluble matrix) as specified above in relation to mineral boards manufacture, already gelled hydraulic binder slurries, such as Portland cement or geopolymers or gypsum, can be converted into the form of non-sticky discrete aggregates or granules are pressed into boards of from 4mm up to 60mm or greater thickness either by calendaring or extruding or more preferably in a continuous double belt press, or alternatively in a single or multi daylight press, in which cohesion is immediate, the board chemistry of hydration going to completion after processing and any resin coalescence or cross-linking or other chemical reaction until final desiccation (inclusion of graded aggregate similar in size to the granules, i.e. 2 to 8 mm diameter, is a useful cost management option).