WO2000078675A1

WO2000078675A1 - Metal-rich silica products from geothermal and synthetic aqueous systems

Info

Publication number: WO2000078675A1
Application number: PCT/NZ1999/000090
Authority: WO
Inventors: James Howard Johnston
Original assignee: Geochemistry Research Limited
Priority date: 1999-06-21
Filing date: 1999-06-21
Publication date: 2000-12-28

Abstract

The present invention is directed to methods for the extraction of silica products from aqueous systems, both geothermal and artificial, containing dissolved silica. Extraction to levels below 100 ppm while at temperatures up to in excess of 100 °C are possible. The nature of the silica products differs from those obtained by earlier work of the inventor and, according to the embodiment performed, include both metal rich silica compounds and metal anion-silicate type compounds. Uses of the products include as additives to paper products for improving print and physical properties; in the control of corrosion in metals and especially ferrous metals; and as absorptive or filtering agents.

Description

METAL-RICH SILICA PRODUCTS FROM GEOTHERMAL AND SYNTHETIC AQUEOUS SYSTEMS.

FIELD OF THE INVENTION

The present invention is directed to methods for the extraction of silica products from aqueous systems containing dissolved silica. Extraction to levels below lOOppm while at temperatures up to 100°C are possible allowing the techniques to be used for geothermal waters whose dissolved silica levels are less than the equilibrium solubility of silica at such temperatures.

The present invention is also amenable to the manufacture of silica products from artificial or synthetic aqueous systems, including systems augmenting silica levels in natural water sources with added silica compounds.

The nature of the silica products differ from those obtained by the prior art methods. Additionally, apparently novel metal anion-silicate type compounds have been prepared by the methods herein. Uses of these compounds include the control of corrosion in metals, especially ferrous metals.

BACKGROUND ART

The present invention has been developed with the problems of geothermal systems in mind, though may also be applied to artificially created systems (comprising dissolved silica components - e.g. sodium silicate) as a method of manufacture of silica products. For clarity, the description the specification (except where stated otherwise) will often direct itself to the application of the invention to geothermal systems. However, it is not intended that this be limiting, for it is envisaged that a skilled addressee will be able to apply the teachings herein to all types of analogous aqueous systems - both natural and artificial. Geothermal sources represent an ideal source of starting material. They represent a ready source of reactants and generally represent a waste product of geothermal power generation. In addition the supersaturated silica solutions of most geothermal power schemes cause problems due to silica deposits blocking process equipment, piping, and re-injection wells. Hence the removal of the silica is of benefit to the industry. Prior art documents US5200165, NZ 228472/232170, US5595717 and NZ 245823/247366 represent earlier techniques for the extraction of silica products from geothermal waters. However, while these are effective techniques, they can only reduce dissolved silica levels to the normal solubility levels for silica at the elevated temperatures at which they are performed. This may not remove sufficient silica, which causes problems when the waste water is cooled further for introduction into the environment.

At elevated temperatures the normal equilibrium solubility of silica may be relatively high. In geothermal systems where the prior art extracts silica, the water will typically contain dissolved silica levels exceeding this equilibrium solubility value. A limitation of the prior art processes are that they are generally limited to the extraction of dissolved silica above the equilibrium solubility value - i.e. they cannot easily reduce silica levels to below this equilibrium value which is influenced by both temperature and pH. In such cases the yields may render the processes economically non-viable when compared to synthetic prior art methods of manufacturing silica type products.

The use of lower temperatures allow greater silica extraction due to a lower solubility value. However other problems, such as premature silica deposition in process equipment, is a potential problem when there is cooling to low temperatures.

In some geothermal systems the dissolved silica levels may be below the normal equilibrium solubility levels, so that they remain unextractable by the aforementioned prior art processes. Hence, potentially valuable raw silica products are wasted as they remain in an unextractable dissolved form.

A better understanding of how geothermal systems work, and how this relates to prior art work, is given by the following description. In a geothermal system where water comes into contact with hot rock, the water is heated to temperatures of up to about 350°C and is maintained largely in the liquid phase due to the overlying rock and hydrostatic pressure head. At these elevated temperatures the water in contact with the surrounding rocks, which predominately comprise silicate minerals, interacts with and partially dissolves these mineral components releasing dissolved silica and the associated suite of metal cations into the geothermal water. The silica solubility is governed essentially by the quartz-water system (Fournier and Potter, 1982), which shows for example, that at neutral pH and 300°C some 670mg.kg^_1 SiO₂ and at 250°C about 460mg.kg^" SiO₂ dissolve (Figure 1). The silica solubility has a significant dependence on pH whereby the solubility increases with increasing pH, particularly above about pH=8.5 as a result of the dissociation of orthosilicic acid:

H₄SiO₄ H,SiO₄ ^" + H⁺

(1) and at higher pH due to further dissociation of the silicilate anion H₃SiO ^":

H₃SiO₄ ^" ^=^ H₂Si0₄ ^2_ + H⁺ For alkali-chloride geothermal waters, the pH is generally in the range 6-9 and hence the first dissociation according to reaction (1) above is the most significant.

In general, the silica dissolves to equilibrium saturation solubility for a particular geothermal water. Brine or chloride containing minerals are also present in geothermal reservoirs or the surrounding country rock. These minerals e.g. NaCl are much more soluble than silica and the extent of their solubility is limited by the quantity of the brine minerals available. In practice this results in geothermal waters containing about 1000-2000mg.kg^" CI^" and about 1000-1200mg.kg^" Na together with a range of other alkali metal and alkaline earth metal cations.

Carbonate and bicarbonate are also present in the water due to dissolution of volcanic CO₂ gas or carbonate-containing minerals.

In summary, geothermal water can therefore be considered as a high temperature weak brine solution saturated with dissolved silica. In the utilisation of geothermal water for direct heat recovery or electrical energy production, the high temperature water (predominately as a single fluid phase) is piped to the surface whereupon the pressure is reduced in a controlled manner and about 30% of the mass flow is flashed to provide steam which is used to drive steam turbines and generate electricity. Alternatively, the steam can be used directly as a source of heat energy. In this flashing process the remaining mass flow (about 70%) forms the separated water fraction which is now cooled to a lower temperature determined by the actual flash conditions used. The cooling results from the thermodynamics of the system in which the heat energy contained in the initial geothermal water mass is used to convert about 30% of this water to steam in the flashing process. The removal of water as steam results in a reduction in the volume of water, and together with the lower temperature, usually to 100-150°C, the net effect is that the separated water is now supersaturated in dissolved silica. Hence there is a strong chemical driving force for the silica to precipitate from this water blocking pipes, process equipment, drains and re-injection wells. Unwanted silica deposition is therefore perhaps the single largest constraint to the development and utilisation of geothermal resources.

As the silica which is precipitated is amorphous in its structure (no long range chemical structural order), such precipitation is governed by the amorphous silica-water system (Fournier and Rowe, 1977) (figure 1). After flashing, the silica concentration in water originally at a downhole temperature for example of 300°C, is increased to about 960mg.kg^"1 SiO₂, and at an original downhole temperature of 250°C, is increased to about 660mg.kg^"' SiO₂ (figure 1). For separated water temperature at 100°C the solubility of amorphous silica is 370mg.kg^"' SiO₂. At an ambient temperature of 20°C, the solubility is only HOmg.kg^" SiO₂. This means that for separated water from a downhole temperature of 300°C cooled to 100°C after atmospheric flashing, some 590mg.kg^" SiO₂ can precipitate from solution. These figures will vary for different geothermal waters, as the silica solubilities depend on pH as well as temperature. In general, for a geothermal system with a separated water flow of 1000 tonnes.hr^" , some 5168 tonnes per year of amorphous silica are deposited. This is a substantial quantity and is currently viewed by the geothermal industry as a major problem to be overcome, rather than as a silica resource for potential utilisation. Other such quantities of silica can be similarly calculated for different waters and operating conditions. Overall, substantial quantities of silica are deposited.

The chemistry relating to amorphous silica polymerisation and precipitation has been well studied by a number of workers (e.g. Marsh et al., 1975; Her, 1979; Rothbaum and Rhode, 1979; Makrides et al., 1980; Weres et al., 1980; Harper, 1994; Harper et al., 1990, 1993, 1996, 1997). The kinetics and mechanism of polymerisation and precipitation depend upon water temperature, pH, dissolved silica concentration and dissolved metal cation content. In general, there is an induction time ranging from seconds to hours prior to the onset of polymerisation, which is also dependent upon the above parameters and hence the chemistry and temperature of the geothermal water. The current practice in geothermal resource utilisation is to try and prevent unwanted silica deposition either by the use of higher separation temperatures (up to 150-160°C) or by chemical treatment (acid dosing to reduce the pH and lengthen the induction time for polymerisation, or the addition of sequestering agents). The former practice reduces considerably, the amount of energy which can be recovered and also means that all downstream process equipment, piping and re-injection system must be operated at elevated pressure and temperature. The latter practice is expensive and may also induce corrosion in steel pipework and process equipment.

Harper et al. (1990, 1993, 1996, 1997) have developed proprietary technology to control the silica precipitation to produce silica products with particular structural, chemical and physical characteristics that make them useful for a variety of specific applications, in particular, paper filling and coating, inert carriers, rubber, paint etc. In this technology the geothermal water, supersaturated with silica or an aqueous fluid containing about 400-1400mg.kg^" SiO₂, is aged in the absence of a precipitation agent and at a pH 5-9.5, to form a stable silica sol. A precipitation agent (typically Ca ions) is added to precipitate an amorphous silica product with a Type I, Type II or Type III tertiary network structure.

Type I silica has a network structure wherein the secondary silica particles (formed from the polymerisation and aggregation of primary particles) are linked by interparticle bridges to form the 3D network. The precipitation agent (Ca ions) forms part of the bulk and surface structure of the silica product. Type I silica in this state has been

7 1 • referred to as unreinforced silica and has a surface area of some 150-300m .g^" and an oil absorption value of about 100-130g oil.g^" silica. When Type I silica is exposed to a supersaturated solution of geothermal water where silica polymerisation has not yet occurred, the dissolved silica is recovered onto the Type I network thereby increasing the secondary particle and bridging sizes, and consequently reinforcing the network structure. This product is referred to as Reinforced Type I silica which typically has a reduced surface area of some 50-60m².g^"' and an increased oil absorption value of about 200-250g oil.g^"1 silica, compared with Type I silica. The optical reflectance and light scattering properties are also enhanced. Reinforced Type I silica was shown to be effective in reducing print through and enhancing optical and print quality of paper. (Harper, 1994; Harper et al, 1990, 1996). In Type II silica, the secondary particles are largely independent and there is limited network structure. Type III silica comprises elements of Type I and Type II silica.

The controlled precipitation of geothermal silica using the approach detailed in the teachings of Harper (1994), Harper et al. (1990, 1993, 1996, 1997), relies on the supersaturation of dissolved silica at a particular pH and temperature to provide the initiating and driving force for the polymerisation and precipitation reaction, and the consequent formation of primary, secondary and tertiary aggregate particles. The quantity of silica which can be recovered therefore depends predominately upon the temperature to which the separated water is cooled. At atmospheric flash this is 100°C. In current geothermal field operations it is common to flash the borehole water at a higher temperature, typically 130-150°C, and then recover additional heat energy from the separated water as electricity using binary cycle turbine technology. For geothermal waters where the dissolved silica content is lower (typically 500-600mg.kg^"' SiO₂) and the pH is weakly alkaline (typically 7-8.5), the induction time for polymerisation in the separated water is often long enough to allow the separated water to flow through the heat exchangers of the binary unit with minimal or no silica deposition whilst being cooled to 80°C. At this lower exit temperature and after the induction period, silica polymerisation and precipitation is problematic and hence there is a definite need to remove it prior to re-injection of the separated water. If the water is cooled further in the re-injection pipelines and wells, then there is propensity for further silica deposition. Rothbaum and Anderton (1975) attempted to remove silica and arsenic collectively from a geothermal water with a significant dissolved arsenic content by producing a poorly defined, impure composite calcium-arsenic silicate material. There was no attempt to control the precipitation chemistry and the product characteristics or quality, but rather to simply deal with an environmental problem as this particular water was discharged into a river. They suggested that a possible use for the poor quality product so produced could be calcining it to a brick type ceramic. A number of problems exist in the prior art, most stemming from an inability to reduce silica extraction to a low enough level to render the process economically viable or attractive, or to solve other problems associated with unwanted silica deposition.

It is an object of the present invention to address these problems, or to at least provide the public with a useful alternative. Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.

DISCLOSURE OF INVENTION

"Amorphous metal-rich silica" is defined as being an amorphous silica incorporating metal cations which have been incorporated in at least one of the following manners: as part of its structure, adsorbed to the surface of the silica, or chemically bound to the surface of the silica.

"Desired silica product" is defined as a product made up predominantly of at least one of the following: amorphous metal rich silica compounds, metal rich silicate compounds, and includes within its definition either of the foregoing containing anionic functionalities including either or both metallic and semi-metallic elements.

"Silica anion product" is defined as being a subset of 'desired silica product' and comprises both amorphous metal rich silica compounds, and metal rich silicate compound which contain anionic functionalities including either or both metallic and semi-metallic elements "Preferred reactant silica components" are defined as comprising silicon-oxygen compounds and functionalities which are soluble in the aqueous system. They are generally characterised by being reactive towards chosen metal cations under the preferred conditions of the invention, and are further characterised as not being polymeric compounds of the type formed when dissolved monomeric silica is allowed to age at a pH of below 9.5. Typically the preferred reactant silica components will comprise: silica, silicic acid, silicate ions, and silicilate ions.

"Dissolved reactant carbonate components" shall refer to dissolved carbonate or hydrogen carbonate ions present within the aqueous system. Many geothermal waters contain a significant proportion of these dissolved ions. According to one aspect of the present invention there is provided a method of forming desired silica products in an aqueous system containing at least one dissolved member of a preferred group of reactant silica components comprising: silica, silicic acid, silicate ions, and silicilate ions; and wherein said method comprises the reaction of reactant silica components in the aqueous system with at least one metal ion reactive therewith; and wherein the reaction conditions are adjusted or maintained such that the formation of desired silica products, as herein defined, substantially occur above a pH of 9.5.

According to another aspect of the present invention there is provided a method, substantially as described above, which is performed according to the steps of: i) should the pH of the aqueous system be below 9.5, increasing the pH of the aqueous system above 9.5 prior to any substantial polymerisation of preferred reactant silica components, and subsequently ii) introducing to the aqueous system at least one metal ion reactive with one or more reactant silica components present in the aqueous system.

According to another aspect of the present invention there is provided a method, substantially as described above, which is performed according to the steps of: i) introducing to the aqueous system at least one metal ion reactive with one or more reactant silica components present in the aqueous system, said introduced metal ion being in the form of an alkaline compound such that should the pH of the aqueous system be below 9.5, the pH of the aqueous system is raised above

9.5; the consequential increase in pH to above 9.5 being effected prior to any substantial polymerisation of preferred reactant silica components.

A method of forming a desired silica product in an aqueous system containing at least one dissolved member of a preferred group of reactant silica components comprising: silica, silicic acid, silicate ions, and silicilate ions; the concentration of such being such that the pH of the system exceeds pH =10, and wherein said method comprises the reaction of reactant silica components in the aqueous system with at least one metal ion reactive therewith; the metal ion being in the form of an alkaline compound, or in combination with an alkaline compound, such that at the completion of the reaction with the reactant silica components the pH exceeds =12, and wherein subsequently the pH of the system is reduced to within the range of pH 7 through 10 inclusive.

According to another aspect of the present invention there is provided a method, substantially as described above, in which increase of the pH of the aqueous system is commenced before more than 50% (by weight) of the dissolved preferred reactant silica components have polymerised. More preferably this is commenced prior to 25% have been polymerised, and even more preferably before 10%. Most ideally, the pH is increased before substantially any preferred reactant silica components have polymerised. Determination may be performed by measuring molybdate active silica, which can be quantitatively determined by a standard ASTM test such as detailed in R.K. Her (vide infra).

According to another aspect of the present invention there is provided a method substantially as described above, in which the pH of the introduced metal ion portion is adjusted with acid or alkali to a pH such that when the desired amount is introduced to the aqueous system, the resulting pH is within the range of 11.0 through 13.9 inclusive.

According to another aspect of the present invention there is provided a method, substantially as described above, in which increase of the pH of the aqueous system is commenced before more than 50% (by weight), more preferably before more than 25%, even more preferably below 10%, and ultimately ideally before substantially any, of the dissolved preferred reactant silica components have polymerised.

According to another aspect of the present invention there is provided a method, substantially as described above, in which the concentration of reactant silica components in the aqueous system is at, or raised, to a level such that the silica (SiO₂) concentration exceeds 1000 mgkg^-1, and introducing at least one metal ion reactive to the reactant silica components; and wherein subsequent to reaction between said components the pH is subsequently lowered to within the pH range of 7 through 9 inclusive. According to another aspect of the present invention there is provided a method, substantially as described above, in which either or both: a) the introduced metal ion is in an alkaline form; b) alkaline material is added in addition to the introduced metal ion; the consequence being that the pH of the aqueous system is raised to pH =11 or higher prior to subsequent lowering of the pH.

According to another aspect of the present invention there is provided a method, substantially as described above, in which the concentration of reactant silica components is a silica (SiO₂) concentration within the range of 5000 through 20,000 mgkg^-1 inclusive. According to another aspect of the present invention there is provided a method, substantially as described above, in which the pH is raised to 10 or above for the formation of desired silica products.

According to another aspect of the present invention there is provided a method, susbstantially as described above, in which the aqueous system comprises substantially geothermal water. According to another aspect of the present invention there is provided a method, susbstantially as described above, which includes an extraction step for removing insoluble product, said extraction step being performed when the aqueous system has been cooled to a temperature within the range of 15 through 100°C inclusive, or above 100°C if the water is maintained under pressure. According to another aspect of the present invention there is provided a method, susbstantially as described above, in which, after reaction of the components the level of dissolved preferred reactant components remaining in solution is less than 50mg.kg^" .

According to another aspect of the present invention there is provided a method, susbstantially as described above, in which raising of pH is at least partially accomplished by adding an alkaline material not directly participating in the reaction forming the desired silica products.

According to another aspect of the present invention there is provided a method, susbstantially as described above, in which the alkaline material is a hydroxide of an alkali metal. According to another aspect of the present invention there is provided a method, susbstantially as described above, in which, if the pH is raised to a pH exceeding 11 , there is a subsequent downward pH adjustment after component reaction to a pH within the range of 7 through 10 inclusive.

According to another aspect of the present invention there is provided a method, susbstantially as described above, in which the resulting insoluble products of reaction are substantially free of Type I, II, or III silica products as defined in patents US5200165 or US5595717.

According to another aspect of the present invention there is provided a method, susbstantially as described above, in which in which increase of the pH of the aqueous system is performed before more than 25% (by weight) of the dissolved preferred reactant silica components have polymerised.

According to another aspect of the present invention there is provided a method, susbstantially as described above, in which an introduced metal ion is of an element having a silicate or silica product of lower aqueous solubility than the preferred reactant silica component with which the metal ion reacts.

According to another aspect of the present invention there is provided a method, susbstantially as described above, in which an introduced metal ion is a cation of one of the following elements: Ca, Mg, Al, first row transition metals, Mo, Sn, Cd, Pb, Ba, and second row transition metals.

According to another aspect of the present invention there is provided a method, susbstantially as described above, in which the introduced metal ion is introduced as an oxide or hydroxide of Ca.

According to another aspect of the present invention there is provided a method, susbstantially as described above, in which the introduced metal ion is introduced as an oxide or hydroxide of Mg.

According to another aspect of the present invention there is provided a method, susbstantially as described above, in which an introduced metal ion is introduced in the form of a soluble salt of the element. According to another aspect of the present invention there is provided a method, susbstantially as described above, in which insoluble products are removed from the aqueous system and the remaining supernatant solution is recycled; additional preferred reactant silica components being introduced into solution prior to a repetition of their repeated reaction with introduced metal ions. According to another aspect of the present invention there is provided a method, susbstantially as described above, in which after introduction of the introduced metal ion, the system is allowed to stand for a period allowing the desired products to form and precipitate, and optionally increase in average particle size.

According to another aspect of the present invention there is provided a method, susbstantially as described above, performed in a manner whereby the desired silica products comprise components having either or both of a microfϊbrillar and microplatelike structure, as hereindescribed.

According to another aspect of the present invention there is provided a method, susbstantially as described above, performed in a manner in which the resulting desired silica products comprise components having an oil absorption value exceeding lOOg.oil per lOOg. silica product.

According to another aspect of the present invention there is provided a method, susbstantially as described above, in which oil absorption in the product is controlled by altering pH and the level of added metal ion. According to another aspect of the present invention there is provided a method, susbstantially as described above, in which the proportion of introduced metal ion is within the range of 1 : 1 to 1.4: 1 inclusive of silica to metal measured as a weight ratio, and the pH is maintained within the range of 10.0 to 11.6. According to another aspect of the present invention there is provided a method, susbstantially as described above, in which the proportion of introduced metal ion is within the range of 1.1 : 1 to 1.25 : 1 inclusive of silica to metal measured as a weight ratio.

According to another aspect of the present invention there is provided a method, susbstantially as described above, in which is also introduced, in addition to metal cations, anions including metallic elements.

According to another aspect of the present invention there is provided a method, susbstantially as described above, in which the metal of the metallic anion is a different element from the introduced metal cation.

According to another aspect of the present invention there is provided a method, susbstantially as described above, in which the metal of the metallic anion comprises: Zn, Cr, V, Mo, Ni, Ti, Sn, Fe, Cu, Al, Mn, or Co.

According to another aspect of the present invention there is provided a method, susbstantially as described above, in which anions of more than one metallic element are introduced. According to another aspect of the present invention there is provided a method, susbstantially as described above, in which there is present, in the aqueous system, dissolved reactant carbonate components and wherein an introduced metal cation is reactive to these components to form a substantially insoluble product; the amount of introduced metal cation being sufficient to cater for both the reaction with preferred reactant silica components and dissolved reactant carbonate components.

According to another aspect of the present invention there is provided a method for removing dissolved silica from geothermal waters, or non-geothermal artificial systems with dissolved silica, to a level of less than lOOmg.kg^" of water, said method comprising the conversion of dissolved reactant silica components to a low solubility silica compound of a metal at a pH exceeding 9.5, and removing the precipitated product.

According to another aspect of the present invention there is provided a silica product resulting from a method according to any one of the preceding claims.

According to another aspect of the present invention there is provided a silica product which is a desired silica product as defined herein and is characterised by substantially comprising particles which are either or both platelike, or microfibrillar, in character.

According to another aspect of the present invention there is provided a silica product which is a desired silica product as defined herein and is characterised by having an oil absorption capacity of 1 OOg oil.1 OOg^" silica or greater. According to another aspect of the present invention there is provided a silica product, substantially as described above, when produced according to a method also substantially as described above.

According to another aspect of the present invention there is provided a silica product, substantially as described above, which includes a proportion of either or both a carbonate, or hydrogen carbonate compound.

According to another aspect of the present invention there is provided a silica product, substantially as described above, in which a proportion of the carbonate or hydrogen carbonate compounds are at least partially encapsulated or incorporated into the structures of the precipitated silica products. According to another aspect of the present invention there is provided a silica product, substantially as described above, in which the predominant metal ion present is calcium.

According to another aspect of the present invention there is provided a silica product, substantially as described above, which has an oil absorption capacity of 200g oil.1 OOg^" silica or greater, and comprises a system in which the introduced metal cation is between 1 - 1.4 times the amount (by weight) of dissolved reactant silica components.

According to another aspect of the present invention there is provided a silica product, substantially as described above, which has an oil absorption capacity of 180g oil.1 OOg^"1 silica or greater, and comprises a system in which the introduced metal cation is between 1 - 2 times the amount (by weight) of dissolved reactant silica components. According to another aspect of the present invention there is provided a silica product, substantially as described above, when used for increasing the opacity of paper or film products.

According to another aspect of the present invention there is provided a silica product, substantially as described above, when used for reducing print-through in paper products.

According to another aspect of the present invention there is provided a silica product, substantially as described above, in a coating formulation applied to paper to enhance either or both print quality and surface finish. According to another aspect of the present invention there is provided a silica product, substantially as described above, when used for modifying the physical characteristics of paper or film products.

According to another aspect of the present invention there is provided a paper or film product including a silica product substantially as described above.

According to another aspect of the present invention there is provided an anticorrosive fibre product incorporating a silica product, substantially as described above.

According to another aspect of the present invention there is provided an anticorrosive fibre product substantially as described above, which is a paper based product.. According to another aspect of the present invention there is provided an anticorrosive fibre product substantially as described above, when used for wrapping or separating metal or metal coated articles.

According to another aspect of the present invention there is provided a paper of film product, substantially as described in the preceding paragraph, having anti-tarnish properties.

According to another aspect of the present invention there is provided a silica product, substantially as described above, for use in anti-mould and/or anti-fouling applications, and in which an introduced metal cation was copper.

According to another aspect of the present invention there is provided an anti-mould and/or anti-fouling paint or coating incorporating a copper containing silica product substantially as described in the preceding paragraph.

According to another aspect of the present invention there is provided a silica product, substantially as described above, when used as an absorptive agent for liquids or gases.

According to another aspect of the present invention there is provided a silica product, substantially as described above, whose preparation was optimised for absorption of ethylene.

According to another aspect of the present invention there is provided an absorptive silica product, substantially as described above, which is used to control the ripening of fruit. According to another aspect of the present invention there is provided a packaging element or film incorporating an absorptive desired silica product substantially as described above and in which the ethylene absorptive silica product is held or presented in a manner such that it is accessible to gaseous ethylene or other gases influencing ripening, present in the environment with which it is intended to interact.

According to another aspect of the present invention there is provided a method for preventing the early ripening of fruit comprising introducing an accessible absorptive silica product substantially as described above into the environment of the fruit. According to another aspect of the present invention there is provided an silica anion product produced according to a method substantially as described above which comprises an anion-silicate type compound of a metallic element, the ratios of the anion, silicate and metallic element portions not necessarily being stoichiometrically consistent, and wherein the silicate portion may include silicates, silicilates, and other predominantly silicon-oxygen moieties.

According to another aspect of the present invention there is provided a silica anion product, substantially as described above, in which the anion includes a metallic or semi- metallic element.

According to another aspect of the present invention there is provided a silica anion product, substantially as described above, which includes at least one of: phosphorus, zinc, aluminium, vanadium, chromium, manganese, molybdenum, copper, aluminium, or cobalt.

According to another aspect of the present invention there is provided a silica anion product, substantially as described above, which includes a transition metal element. According to another aspect of the present invention there is provided a silica anion product, substantially as described above, in which the anion comprises the metallic or semi-metallic element in combination with oxygen.

According to another aspect of the present invention there is provided a silica anion product, substantially as described above, in which an anion incorporating a metallic or semi-metallic element was introduced during its preparation.

According to another aspect of the present invention there is provided a silica anion product, substantially as described above, in which the introduced anion was at least one member of a group comprising: a member of the phosphate group, a vanadate, a molybdate, a permanganate, a manganate, a member of the chromate group, or a cobaltate.

According to another aspect of the present invention there is provided a silica anion product, substantially as described above, for use as an anticorrosive agent for ferrous metals.

According to another aspect of the present invention there is provided an anticorrosive paint or coating product incorporating a silica anion product substantially as described above.

According to another aspect of the present invention there is provided an anticorrosive paint or coating product incorporating a silica product substantially as described above. According to another aspect of the present invention there is provided a method for protecting ferrous metals comprising the deposition of either or both a silica anion product or a desired silica product, both substantially as described above, on to a surface of said metal.

According to another aspect of the present invention there is provided a silica product, substantially as described above, which has been modified to exhibit hydrophobic properties.

According to another aspect of the present invention there is provided a silica product, substantially as described above, in which the silica product has been reacted with a C₄ or greater alkyl alcohol. According to another aspect of the present invention there is provided a silica product, substantially as described above, when added to rubber to alter its physical properties.

According to another aspect of the present invention there is provided a silica product, substantially as described above, when used in pet litter products.

According to another aspect of the present invention there is provided a silica product, substantially as described above, when used as a filtering, adsorptive, or absorptive agent for non-particulate matter in fluids and/or gases.

According to another aspect of the present invention there is provided a silica product, substantially as described above, when used as a filtering agent for particulate matter in fluids and/or gases. According to another aspect of the present invention there is provided a silica product, substantially as described above, when used as a selective absorbent or filtering agent in cigarettes.

According to another aspect of the present invention there is provided a silica product, substantially as described above, when used to selectively absorb oils or a hydrophobic liquid in the presence of water or another hydrophilic liquid.

According to another aspect of the present invention there is provided a silica product, substantially as described above, when used in cosmetic formulations and products.

According to another aspect of the present invention there is provided a silica product, substantially as described above, when used in natural pharmaceutical formulations and products.

According to another aspect of the present invention there is provided a silica product, substantially as described above, when used as a moisture control agent in soils and potting mixes.

According to another aspect of the present invention there is provided a silica product, substantially as described above, when used as an antiblocking agent and/or filler in plastics.

There are a number of differences between the present invention and prior art processes such as those described in NZ228472/232170 and NZ 245823/247366 for the extraction of silica from geothermal waters. In simple terms these earlier processes focused on the polymerisation of soluble monomeric silica by ageing while maintaining the pH below 9.5. The insoluble polymeric product was readily removed from the system as a precipitate. The methods suffer some disadvantage due to the time period required for the ageing step - a significant problem when dealing with large continuous volumes of water - and being unable to remove silica to levels below the normal solubility of silica for the process conditions.

In contrast the present invention, as will become clearer from the ensuing description, utilises a different reaction system to extract dissolved silica components (the preferred reactant silica components) from the aqueous system. In simple and general terms, this comprises the conversion of the dissolved silica components into different compounds whose solubilities are typically significantly less than the original silica components. This allows for not only much higher extraction rates but also the use of starting materials having dissolved silica levels which were considered too low for the identified prior art processes. The nature of the product also differs and thus the present invention is also applicable to aqueous systems, including synthetic systems, with high levels of dissolved silica.

The difference in the chemistry of the systems is exemplified by a minimum pH of 9.5 in the preferred embodiments of the present invention. Further, the desired reactions of the present invention require non-polymerised starting reactants and thus the present invention avoids as much as possible the reaction conditions of those identified prior art processes.

These differences will become more apparent from the following description which will also make reference to the attached drawings. BRIEF DESCRIPTION OF DRAWINGS

Figure 1 illustrate Quartz and Amorphous Silica Solubility, as per Harper (1994)

Figure 2 are Transmission Electron Microscope Photographs Showing the

Microfibrillar and Microplate Structure of Amorphous Calcium Rich Silica/Silicate from the present invention.

Magnification: 105,000x or lcm=100nm=0.1 microns.

Figures 3 are Transmission Electron Microscope Photographs Showing the Microfibrillar and Microplate Structure of Composite Calcium Carbonate - Calcium Rich Silica/Silicate. Magnification: 105,000x or lcm=100nm=0.1microns.

Photographs (a) and (b) show discrete microcrystals of calcium carbonate surrounded by free microfibrils and microplates of amorphous calcium rich silica/silicate. Photographs (c) and (d) show the microfibrils and microplates of amorphous calcium rich silica/silicate bound to or closely associated with the calcium carbonate microcrystals.

BEST MODES FOR CARRYING OUT THE INVENTION

The Precipitation Process

This patent describes new technology where the silica is recovered from geothermal water or an aqueous solution containing dissolved silica (silicic acid), as a desired silica product as defined above. When the metal cation is calcium the novel amorphous calcium rich silica or amorphous calcium silicate has a particular microplatelike and/or microfibrillar structure (Figure 2). If sufficient quantities of dissolved carbonate or bicarbonate are present in the water, a further novel composite calcium carbonate - calcium rich silica/silicate product is formed. For metals other than calcium the novel amorphous metal rich silica or amorphous metal silicate generally comprises either spherical or acicular microparticles which are agglomerated in the solid product.

The water is typically at a temperature of 60-80°C but may range from about 15°C up to 100°C if the water is at atmospheric pressure, or indeed at temperatures considerably above 100°C if the water is maintained under pressure. In this technology the pH of the water is rapidly increased to above pH=9.5, preferably pH=T0-13 and the novel amorphous metal rich silica/silicate or composite metal (e.g. calcium) carbonate - metal rich silica/silicate product is formed by the rapid addition of suitable quantities of the metal ion e.g. Ca , ideally before the onset of silica polymerisation. Silica polymerisation will reduce yields of desired silica products and should ideally be minimised. While some embodiments and applications may tolerate large amounts of polymerised product (e.g. up to 50%), keeping it below 25%, and more ideally 10% is preferred. The product rapidly forms a fine suspension in the water and then the particles grow and aggregate to form larger particles or floes which readily settle out of solution. The novel amorphous metal rich silica/silicate or composite calcium carbonate - metal rich silica/silicate product (of this example) can then be recovered as a concentrated slurry, then optionally filtered, optionally dried, and optionally milled, depending upon the actual application desired.

At this increased pH the dissolved silica, which is often considered as silicic acid H₄SiO , is dissociated and is present largely as the silicilate anion H₃SiO₄ ^" according to the reaction (1) which has a pK_a = 9.8 (25°C):

H₄SiO₄ --=-=---- H₃SiO₄ ^" + H⁺ (1)

Also, the polymerisation is essentially inhibited due to the significantly increased silica solubility at this increased pH. This increase in pH therefore provides a method by which silica precipitation can be largely prevented.

This novel approach described here for the recovery of silica is based on the fact that under increased alkaline conditions, greater than about pH=10, the silicilate anion H₃SiO₄ ^" reacts rapidly with certain metal cations, e.g. alkaline earth Ca , Mg , Sn etc., Al³⁺, transition metals e.g. Cr³⁺, Mn^2+/3+, Fe^2+/3+, Co^2+/3+, Ni^{2+ 3+}, Cu^+/2+, Zn²⁺, Mo ⁺, Ti ^{+ +} to form amorphous metal rich silicas/silicates.

The two most important steps in this new technology are the rapid increase in pH and the rapid addition of the appropriate metal cation. Typical metal cations are those of the above mentioned alkaline earth Ca , Mg , Sn etc., Al , transition metals Cr ,

M_Λn 2+/3+ , _ϋ Fe 2+/3+ , ^ Co 2+/3+ , Cu +12+ , N_τi-2+/3+ , Z -_.n 2+ , _Λ M_fo 2+ ei .t.,her as si •ng ,le ent .i.t.i.es or in combinations of two or more entities, e.g. Ca /Zn , Ca /Al , Ca /Zn /Al , Ca²⁺/Cu²⁺ etc.

This novel approach enables these novel substantially amorphous metal rich silica/silicate products to be rapidly precipitated with the microstructure described here, before the dissolved silica can polymerise and yield a precipitated silica with a Type I, Type II or Type III tertiary structure in accordance with the earlier process described by Harper (1994), Harper et al. (1990, 1993, 1996, 1997).

9+

For example, in this new technology, if Ca is used as the metal cation, then the overall reaction may be considered in simple and broad terms as:

H₃SiO₄ ^" + OH^" + Ca²⁺ ^=------ CaSiO₃ + 2H₂O (3)

However, the actual stoichiometry of the amorphous CaSiO₃ product varies significantly

9+ depending upon the quantity of Ca , H₃SiO ^" (content of dissolved silica) and the pH (content of OH^") and is therefore more accurately considered as a calcium (metal) rich amorphous silica/silicate. The chemical and physical properties also vary accordingly (e.g. see Tables 1-5).

In the new technology described in this patent, it is important for the dissolved silica (if it is to form the desired silica products) to be in an unpolymerised state (essentially as the H₃SiO₄ ^" ion) and that the pH is raised rapidly to a pH exceeding 9.5, and preferably exceeding pH 10, and most preferably within the range of pH=10 through 13. The

2- metal cation (Ca ) is added to precipitate the amorphous calcium rich silica/silicate product with a microplatelike or microfibrillar structure. Such amorphous calcium rich silica/silicate products essentially do not form at pH values less than about pH=10.

1 2+ For a water containing about 800mg.kg^" SiO₂, the Ca is added in an amount in excess of 150mg.kg^" Ca but preferably 500-1600mg.kg^" Ca in the water, depending upon the chemical and physical characteristics required of the product. For a water containing about 500mg.kg^" SiO₂, the Ca is added in an amount in excess of 150mg.kg^" Ca but preferably 300-1000mg.kg -1 Ca 2+ in the water, and for a water containing only about 200mg.kg^" SiO , the Ca is added in an amount in excess of 150mg.kg^" Ca ⁺ but

1 2+ preferably 200-500mg.kg^" Ca in the water. In many cases the residual dissolved silica concentration in the water following silica precipitation is less than lOmg.kg^"1 SiO₂. A suite of process examples is given in Tables 1 and 2.

For waters containing dissolved silica which has been provided by adding a soluble silicate to the water, for example sodium silicate, the silica concentration can be increased up to at about 200,000mg.kg^"' SiO₂, preferably between 5,000-50,000 mg.kg^"1 SiO₂ with

2+ 9+ the Ca being increased proportionately to maintain a similar SiO₂:Ca ratio as that above for a water containing 800 mg.kg^" SiO₂. The temperature at which the reaction can be carried out (temperature of the silica containing water) can be from about room temperature up to about 100°C, or higher if the water is maintained under pressure.

Precipitation of these metal rich silica/silicates is favoured at increased alkalinity as the pH is further increased from preferably pH=10 to preferably pH=13 which is the pH region where the required H₃SiO₄ ^" ion predominates. Below a value of pH=10 the substantial formation of the novel metal rich silica/silicates is not favoured. Above a value of pH=13 gel reactions predominate. These reactions are not preferred, though the subsequent conversion of these to desriable products, in high silica aqueous systems is given below.

When using solutions with a higher dissolved SiO₂ concentrations, the pH of the solution increases from about pH=10 up to about pH=12.5. The pH of a solution with a dissolved silica concentration of about 20,000 mg.kg^"1 SiO₂ at room temperature is about

2+ pH=12.2. If the Ca is then added as a Ca(OH)₂ slurry and in a similar 0.8-1.4

2+ 1

SiO₂:Ca ratio to that for the 1000 mg.kg^" SiO₂ solutions, the pH increases further. For a 20,000 mg.kg^"1 level of Ca²⁺ added as Ca(OH)₂ to this 20,000 mg.kg^"1 solution of dissolved silica, the pH of the resulting mixture and at which the amorphous calcium silica/silicate product forms is about pH=13.8.

For a solution with a dissolved silica concentration of 5,000 mg.kg^" SiO₂, the pH at

1 2+ room temperature is about pH=11.6. When a 5,000 mg.kg^" level of Ca added as Ca(OH)₂ to this 5,000 mg.kg^"1 solution of dissolved silica, the pH of the resulting mixture and at which the amorphous calcium silica/silicate product forms is about pH=12.8. Further examples are presented in Table la.

Due to the high pH, the product stability field is shifted from that of a microfibrillar type product to a more gel type product with the consequent lowering of the oil absorption. An amorphous calcium silica/silicate product made from a solution at room temperature with a dissolved silica concentration of 5,000 mg.kg^" SiO₂ and 5,000 mg.kg^"

1 9+ 1 Ca has an oil absorption of 160-190 g oil.1 OOg^" , whereas a product made from a solution at room temperature with a dissolved silica concentration of 20,000 mg.kg^" SiO₂ and 20,000 mg.kg^"1 Ca²⁺ has an oil absorption of 130-140 g oil.1 OOg^"1.

This alteration in the properties of the product has been found to be readily addressed by subsequently lowering the pH of the system. By adjusting the pH of the amorphous calcium silica/silicate slurry or the moist filter cake to a lower value, such as by the addition of acid after formation, it is possible to remove the gel type material and increase the oil absorption of the amorphous calcium silica/silicate material accordingly due to the more dominant microfibrillar structure. For example, if the slurry of the above

1 1 9+ product made from a solution of 5,000 mg.kg^" SiO₂ with 5,000 mg.kg^" added Ca is adjusted to pH=9.0, the resulting dried amorphous calcium silica/silicate product has an oil absorption of about 250 g oil.1 OOg^" , and if it is adjusted to pH=8.0 the oil absorption increases further to about 300 g oil.1 OOg^"1 (Table la).

Accordingly the versatility of the system is enhanced to accommodate reactions involving high silica concentrations with alkaline materials for introducing the metal ion. This allows the reaction to operate in a region where previously undesirable products were formed, and to convert these products into highly useful desired silica products. Such modified methods, involving subsequent pH lowering, are not restricted to calcium systems but can be applied also for other preferred metal cations as described herein.

In addition, it is also possible to control the pH of the added Ca²⁺ slurry/solution by using for example an appropriate mix of Ca(OH) and acid. Another option is to use other calcium salts, in combination with a suitable alkaline material to allow the system to attain the preferred pH. One possible example is the combination of CaCl₂ with NaOH, or similar such reagents. The use of alternative compounds to the calcium hydoxide also allows the use of higher solubility calcium compounds which can be beneficial when high reactant concentrations are used. These alternatives can also assist in reducing the amount of gel material in the final product. If pH adjustment of the resulting amorphous calcium silica/silicate slurry or the moist filter cake is also carried out, then it is possible to increase the oil absorption to about 350 g oil.1 OOg^"1. Further examples are presented in Table la.

While calcium has been described as the metal ion of interest, other metal cations such as described herein may also be substituted, either partially or entirely, for calcium.

Simultaneous Increase of pH and Metal Cation

A convenient way to increase the pH rapidly and simultaneously rapidly provide a source of metal cations is by using an appropriate metal hydroxide, for example calcium hydroxide (Ca(OH)₂). Such hydroxides are generally sparingly soluble in water and are best added as a slurry to the (usually hot) geothermal or silica-containing water. Upon addition, the hydroxide particles dissolve wherein the OH^" ions produce a spontaneous

1+ increase in pH to the required level and the metal ions (Ca ) react with dissolved silica (silicilate ion) according to equation (3), essentially simultaneously. Fine adjustments to the pH can be made but subsequent rapid addition of base or acid. Alternatively, a soluble salt of the metal may be added, for example calcium chloride (CaCl₂) and the pH adjusted upwards to the desired value by the rapid and essentially simultaneous addition of base (sodium hydroxide, NaOH). In this approach the base may be added first

9+ followed by the rapid addition of the metal (Ca ) ions or vice versa.

The metal-rich silica/silicate begins to form almost immediately and with continued gentle stirring usually forms large floes that settle readily. The majority of the reaction is completed in the first 1-5 minutes of reaction time, and the reaction is fully complete after 10-20 minutes, depending upon the reaction temperature and chemical conditions. In general, the use of a metal hydroxide (Ca(OH)₂) to provide both the metal ions and the hydroxide ions is more cost effective than using a separate metal-containing salt and a separate base for pH adjustment, and hence is the preferred method of practising the technology.

Almost immediately after the Ca(OH)₂ is added to the silica-containing water (which for the purposes of this illustrative example has a dissolved silica content of 800 - 1,000 mg.kg -¹ SiO₂₎ the pH increases rapidly to a value between about pH=10.3-1 1.6, typically or preferably about pH=10.5-11.3, and then increases slowly over about a further 0.5pH units during the formation and precipitation of the calcium rich silica/silicate product.

A number of examples of the precipitation conditions where these amorphous metal rich (mainly calcium) silicas/silicates, and the properties and compositions of the resulting products are shown in Tables 1-5 below. Examples of the use of some of these products in different applications are also presented below.

This new technology is significantly different from that described in the teachings of Harper (1994), Harper et al. (1990, 1993, 1996, 1997) where the dissolved silica (H₃SiO₄ ^") is polymerised in a controlled ageing process at a pH less than pH=9.5 to produce spherical secondary silica particles, prior to their precipitation as an amorphous silica product with a Type I, Type II or Type III tertiary network structure.

The process chemistry and product characteristics of material produced by the teachings of the new technology are therefore distinctly different from those of Harper (1994), Harper et al. (1990, 1993, 1996, 1997)

Low Solubility of Metal (Calcium rich silica/silicate and Enhanced Silica Recovery

The solubility of these amorphous metal (calcium) rich silica/silicate products is substantially less than that of amorphous silica (Type I, Type II and Type III) at the same temperature and pressure. Thus the total amount of silica removed from the geothermal water or another silica-containing water is correspondingly significantly greater using the new technology presented here. Experimental work has shown that by practising this new technology, the dissolved silica concentration can be reduced to below about 20mg.kg^" SiO even for water at 100°C. If the added Ca²⁺ content is preferably greater than about 1.2 times the dissolved SiO₂ content and the pH is preferably greater than pH=l 1, then it is possible to remove essentially all the dissolved silica from the water (e.g. see Table 1). This compares extremely favourably with the equilibrium silica solubility of about 370mg.kg^"1 SiO₂ at 100°C which essentially represents the lower limit to which silica can be removed from geothermal water by the technology of Harper (1994), Harper et al. (1990, 1993, 1996, 1997). By using the teachings claimed in this patent application it is possible to remove substantially all or the greater part of the dissolved silica from geothermal water, even at temperatures up to 100°C at atmospheric pressure, or indeed considerably above 100°C if the water is maintained under pressure. This means that the propensity for further silica deposition from the separated water in downstream pipelines, process equipment and re-injection wells is eliminated, even if the water is cooled to ambient temperature. Such a process offers substantial advantages to geothermal energy utilisation.

A desirable consequence of this reduced residual dissolved silica content is that this new technology enables a substantially greater amount of metal rich silica/silicate product to be recovered from the same volume of separated geothermal water, compared with the amount of precipitated Type I, Type II or Type III silica that can be recovered using the technology of Harper et al. (1990, 1993, 1996, 1997). For example, using this new technology claimed here, if geothermal water with downhole temperature of 300°C is cooled to 100°C after atmospheric flashing some 940mg.kg^" SiO₂ can be recovered from the water. This compares with about 590mg.kg^" SiO₂ that can be recovered from the water using the technology of Harper et al. (1990, 1993, 1996, 1997).

As the product of the new technology is a metal rich silica/silicate, the total mass of material is further increased due to the metal ion and hydroxyl water content of the product. If the product is a composite calcium carbonate - calcium rich silica/silicate material the mass of product recovered is increased further. Experimental work has shown that a product weight equivalent to about 2.0-3.5 times the recoverable silica content can be produced from the separated water. Therefore for the above geothermal water with an initial silica content of 940mg.kg^"1 SiO₂ and a flow rate of 1000 tonnes.hr^" there is the potential to be able to produce some 15,400-27,000 tonnes per year of this novel composite calcium carbonate - calcium silica/silicate product per year. This much larger quantity of available product significantly enhances the economics of a commercial silica recovery operation.

Relation Between Oil Absorption and Precipitation Conditions of the Novel Calcium Rich Silica/Silicate Products Formed From Waters Containing about 750-1400 mg.kr Dissolved Silica The data presented in Tables 1 and 5 show that for waters with a particular dissolved silica concentration of about 750-1400 mg.kg^" SiO₂, the oil absorption of an obtained calcium-rich silica/silicate product generally increases with increasing pH, and is greatest for products produced at an initial formation pH of preferably between pH=l 0.5- 11.3. In addition, the oil absorption is generally higher for products which have been produced

9+ under conditions where the added Ca content is equal to or slightly greater than the dissolved silica content, where preferably the amount of added Ca ⁺ content is between 1-1.4 times the amount (weight basis) of dissolved SiO₂ in the water. Products with the highest oil absorption, generally greater than or equal to 200g oil.1 OOg^" product, are

9+ obtained where the amount of added Ca is preferably 1.1-1.25 times the amount (weight basis) of dissolved SiO₂ in the water. Process examples detailing this observation for a water at 60°C containing 800mg.kg^" dissolved SiO₂ wherein the novel calcium-rich silica/silicate products are precipitated

-1 2+ using amounts of Ca(OH)₂ slurry between 750-1200mg.kg^" Ca are presented in (Table 5). The data in Table 5 show there is a broad maximum in the oil absorption over a range

2+ 1 2+ of added Ca levels from about 900-1050mg.kg^" Ca with lower oil absorption being

2+ obtained at both lower and higher Ca levels. Similar trends are observed in the process

2+ examples for waters with other dissolved silica levels and amounts of added Ca as presented in Table 1. However the products with the highest oil absorption are generally produced from waters containing amounts of dissolved silica that are preferably greater than SOOmg.kg^"1 SiO₂. Products with a high oil absorption are useful for paper filling, paper coating and inert carrier applications etc.

If a product with a lower oil absorption is required, such as a flatting agent in paint, the

9+ added Ca content should generally be less than the dissolved silica content (on a weight basis) and the initial formation pH should be less than about 10.5 and preferably about 10.0.

Table 5 also shows that for waters with a dissolved silica concentration of about 750- 1400 mg.kg^" SiO₂, the yield of the novel calcium-rich silica/silicate product increases

2+ progressively with increasing added Ca . For the water characteristics and precipitation conditions pertaining to these particular products, those with the highest oil absorption have yields of 2.9-3.2 kg of product per kg of dissolved silica. As previously mentioned, these yields are substantially greater than those for Type I silica products produced according to the technology of Harper et al (1990, 1993, 1996, 1997) for processing the same volume of water with the same dissolved silica content. Much of the capital and operating costs of recovering silica from geothermal water is associated with the requirement of having to process very large volumes of hot water (up to about 3000 tonnes/hr^" ). Therefore, this new technology presented here which produces a novel calcium-rich silica/silicate product with similar oil absorption and other performance properties as those produced according to the teachings of Harper et al (1990, 1993, 1996, 1997), provides a substantial economic and competitive advantage over the technology of Harper et al (1990, 1993, 1996, 1997).

For solutions containing dissolved silica contents greater than about 1400 mg.kg^" SiO₂, the oil absorption of the product is controlled by the added Ca²⁺ content, the pH at which the formation of the amorphous calcium silica/silicate product takes place and the pH of the final slurry or filter cake product. This is discussed in detail above.

Relation between Oil Absorption and Precipitation Conditions of the Novel Zinc Rich Silica/Silicate Product

A number of novel zinc rich silica/silicate products have been formed using water containing lOOOmg.kg^" dissolved SiO at 60°C to which an amount of a 20,000mg.kg^"

9+ 1 1+

Zn solution was added to give a level of 300, 600 and lOOOmg.kg^" Zn in the silica solution respectively and the pH was then rapidly adjusted to greater than pH=10.0 to precipitate the particular products. The various precipitation conditions and the oil absorption of the respective novel zinc rich silica/silicate products are detailed in Table lb. High resolution electron microscopy showed the products to comprise loosely agglomerated spherical microparticles.

The data presented in Table 2 show that the oil absorption is about lOOg oil.1 OOg^" product, which is substantially lower than the oil absorption for calcium rich silica/silicate products produced under similar precipitation conditions (Tables 1 and 5). This is in fact very advantageous to the use of the product as an anticorrosion agent in paint wherein a high oil absorption is undesirable.

This study further exemplifies the importance of the novel microfibrillar and microplatelike structure as exhibited by the calcium rich silica/silicates in imparting a high oil absorption to the product.

Composite Calcium Carbonate - Calcium Rich Silica/Silicate

As introduced above, if calcium is used as the metal ion then for geothermal waters containing appreciable quantities of dissolved carbonate or bicarbonate ions, calcium carbonate is readily deposited as the pH is increased. The deposition of carbonate takes place and is essentially complete as the pH is increased to about pH=9.5-10 according to the reaction:

Ca²⁺ + HCO₃ ^" + OH^" > CaCO₃ + H₂0

If the pH is increased rapidly the calcium carbonate will form as very small (micron to sub micron size) crystals, which will not grow further in size as all the bicarbonate ions are used up in the initial rapid precipitation.

For geothermal waters that are relatively low in dissolved silica and relatively high in bicarbonate, the resulting product may contain up to about 60% CaCO₃ (e.g. EF products, Table 4).

As most geothermal waters contain some dissolved bicarbonate, the product produced by practising this new technology is generally this composite calcium carbonate - calcium rich silica/silicate material. As sodium silicate also generally contains quantities of carbonate and bicarbonate components (often formed by reaction of excess sodium oxide with the CO₂ in the air), silica-containing solutions produced from sodium silicate also yield a composite calcium carbonate - calcium rich silica/silicate product.

High resolution transmission electron microscopy has shown that as well as the existence of discrete microcrystals of CaCO₃, many of the microcrystals of CaCO₃ are surrounded by microfibrillar amorphous calcium rich silica/silicate material (Figure 3). Accordingly, this composite calcium carbonate - calcium rich silica silicate product produced by the practise of the new technology described here is also novel. Examples of these products are given in Tables 1,2 and 5 below.

Recovery of Various Composite Calcium Carbonate - Calcium Rich Silica/Silicate Products From Water From the Kawerau Geothermal Field. New Zealand.

A range of composite calcium carbonate - calcium rich silica/silicate products have been recovered from the separated waters of the East Bank of the Kawerau Geothermal field, New Zealand, using the new technology described in this specification. In this field the separated water flows through a binary cycle electricity generating plant into a large lagoon and is then discharged into the Kawerau River. The water for these process examples was taken immediately from the exit side of the binary cycle plant. The temperature was typically about 90°C and the dissolved silica concentration about 700 mg.kg^" SiO₂.

9+ Table lb shows the results of a suite of extractions where a particular level of Ca was added to the geothermal water in the form of a Ca(OH)₂ slurry under vigorous mixing. The composite calcium carbonate - calcium rich silica/silicate product was formed immediately and the reaction was essentially complete in a few minutes.

The data (Table lb) show in general that as the level of added Ca as Ca(OH)₂ increases, the inherent pH buffering effect of the geothermal water is gradually overcome by the alkalinity of the Ca(OH)₂ and the oil absorption and yield of the resulting composite calcium carbonate - calcium rich silica/silicate product increases accordingly. The inherent calcium carbonate component of the product is formed from the reaction of the

9+ dissolved bicarbonate/carbonate with the added Ca at alkaline pH. The maximum oil absorption achieved was 177 g oil.1 OOg^"1, which is below that obtained for synthetic sodium silicate containing waters of a comparable concentration (Table 1).

1 9 +

After about 1000 mg.kg^" of added Ca the ISO brightness remains essentially unchanged at a value of about 93, which is ideally suited for a number of applications such as paper filling and coating, and a paint additive, where optical properties are important. Transmission electronmicroscopy showed this composite calcium carbonate - calcium rich silica/silicate product to comprise a mix of blocky calcium carbonate and microfibrillar calcium silica/silicate. However, at the lower levels of added Ca(OH) and hence lower pH, the calcium carbonate component dominated the product. With increasing pH due to the increasing level of added Ca(OH)₂, the microfibrillar calcium silica/silicate becomes more dominant.

9 +

Table lc shows the effect of adding both Ca as Ca(OH)₂ and sodium hydroxide (NaOH) to the geothermal water to increase the pH to a value that favours the formation of microfibrillar calcium silica/silicate. However, due to the dissolved level of bicarbonate/carbonate in the water, calcium carbonate still forms. The data clearly show the importance of increasing the pH to a value greater that about pH=10 in order to produce a composite calcium carbonate - calcium rich silica/silicate product with a suitably high oil absorption. This optimum increased pH cannot be achieved solely by the addition of Ca(OH)₂ alone, and requires the addition of NaOH as

9+ well. For a particular level of added Ca , due to the pH buffering effect of geothermal water, the effect of adding an increased level of NaOH above that to raise the pH to a value of about pH=10.5, has little affect on the oil absorption of the resulting product.

The product with the highest oil absorption (235 g oil.lOOg^" ) and brightness (94.1)

1 2+ values was achieved using 1000 mg.kg^" Ca and an added NaOH content of 500 mg.kg^'

, at a pH=10.6 (Table lc). However, products with oil absorptions in the range of 200 g oil.1 OOg^" and a brightness of 93-94 can readily be produced under a range of conditions,

2+ 1 eg. levels of Ca (added as Ca(OH)₂) from about 800-1200 mg.kg^" and appropriate levels of NaOH (Table lc). In general, with this approach, the oil absorption begins to

9+ 1 decline at added Ca levels of greater than about 1500 mg.kg^" . A transmission electronmicroscope study of these higher oil absorption products show a greater development of the microfibrillar calcium silica/silicate structure.

The resulting composite calcium carbonate - calcium rich silica/silicate product can be recovered as a slurry or a filter cake, or optionally in dried powder form depending upon the particular end use application.

Recycling of the Residual Water after Processing When geothermal water is used to provide the source of dissolved silica, the residual water usually contains very low concentrations (low mg.kg^" quantities) of a significant number other dissolved species. Once the silica content of the water has been recovered as novel calcium (metal) rich silica/silicate and or composite calcium carbonate - calcium (metal) rich silica/silicate products by the new technology presented here, the residual water is usually reinjected or discharged to surface waterways. As mentioned above, the flow rate for geothermal systems is typically of the order of 500-3000 plus tonnes.hr^" of water, and hence any process to recover dissolved silica must be able to handle these high flow rates.

However, if the source of dissolved silica is an aqueous solution of sodium silicate then the relatively low dissolved silica concentrations used similarly, mean that large quantities of water must also be processed in order to obtain significant quantities of product. As it would generally be uneconomic to utilise and dispose of such large quantities of fresh water and residual process water respectively, it is essential to recycle the residual water to the front of the process for re-use. This approach has been successfully demonstrated whereupon a quantity of fresh water was heated to 60°C and to it was added sufficient sodium silicate to provide a dissolved silica concentration in the water of 800mg.kg^" SiO₂. A quantity of Ca(OH)₂ slurry was

1+ 1 then added with rapid stirring to provide a Ca concentration of lOOOmg.kg^" and a pH=10.3-11.6, preferably pH=10.5-11.3, in the mixed solution. The formation of the novel calcium rich silica/silicate product commenced immediately and the reaction proceeded to completion over a further 10 minutes. The dilute slurry was then allowed to settle in a clarifier vessel. The concentrated slurry was taken from the base of the vessel and the clear supernatant water from the top. The slurry was then filtered to provide a cake which could be used in this form or dried to a powder form. Chemical analyses of the combined supernatant and filtrate water showed that this water typically contained a residual dissolved silica content of 5-20mg.kg^" SiO₂ and about

1 2+

200-3 OOrng. kg^" Ca . A quantity of fresh water was added to make up for the loss due

9+ to slurry separation and filtration. The Ca concentration of this recycled water stream was then increased to lOOOmg.kg^" Ca and reheated to 60°C. The pH was then adjusted to a level such that when the required amount of sodium silicate was added to increase the level of dissolved silica to δOOmg.kg^"1 SiO₂, the desired pH value of preferably pH=l 0.5- 11.3 was maintained. The formation of the second quantity of novel calcium rich silica/silicate product again commenced immediately. The reaction was allowed to go to completion over a further 10 minutes, the slurry settled to provide the product and the supernatant water recycled to the front end of the process again. This overall process is thus operated in a continuous manner.

This recycle process is important when the precipitating cation is zinc or some other heavy metal rather than calcium, which should not be released to the environment.

Composite Calcium (Metal) Silica-Anion Products

Prior to or during the reaction between the metal cation and the H₃SiO₄ ^" ion, it is possible to introduce one or more anions into the reaction system. In these situations the metal cations act as bridging agents and bond the silica-containing anion with the other anion(s) that have been introduced to the reaction system.

For example, phosphate anions have been added to a solution of dissolved silica and with

1+ a rapid increase in pH and addition of Ca ions according to the teachings of this new technology, a novel amorphous composite calcium phosphate-silicate product is

2+ precipitated. If Zn is used as the cation, a similar amorphous composite zinc phosphate-silicate is precipitated.

Other examples of such composite products which have been successfully prepared are zinc vanadate-silicate, calcium vanadate-silicate, calcium permanganate/manganate- silicate, calcium chromate-silicate and calcium molybdate-silicate. In these cases the anion is added to the silica-containing water, followed by the rapid addition of the metal cation with subsequent rapid pH adjustment. The amount of added anion is typically comparable to that of the dissolved silica or metal cation level. However, these levels can be varied accordingly to provide products with significantly different compositions, depending upon their ultimate use. A number of process examples are presented in Table 2.

Chemical Exchange of Surface Metal Cations and Corrosion Resistance and Protection

The metal cations perform a functional role in both the formation of the amorphous metal rich silica/silicate product according to reaction (3) above, and also in adsorbing or chemically bonding to the silica/silicate surface by displacement of the H⁺ ions on the -Si-OH silanol groups with a simultaneous modification of the surface charge.

Ca²⁺ + -Si-OH ^> -Si-O-Ca⁺

or Zn²⁺ + -Si-OH ^ -Si-0-Zn⁺

Under appropriate conditions, these metal cations may be exchanged for other metal ions or hydrogen ions. This exchange therefore provides a mechanism whereby these novel products are able to provide corrosion inhibition to a metal surface.

Corrosion of metals involving dissolved oxygen in the water is invariably an electrochemical process which takes place on a microstructural scale at compositional or structural irregularities on the metal surface. The inherent electrical conductivity of the water provides the pathway of electron transfer between the anode and cathode sites. This conductivity is greatly enhanced by the presence of dissolved salts such as sodium chloride (sea water) or acid rain.

The corrosion of metals, for example iron (Fe) or steel is an electrochemical process. Iron

2+ dissolves as ferrous (Fe ) ions at the anodic site and is then further oxidised to ferric (Fe ⁺) ions.

Anode Fe — -^■ Fe ⁺ + 3e This reaction is coupled with the reduction of dissolved oxygen at the cathodic site.

Cathode O₂ + 2H₂O + 4e → 4OH^"

The Fe ⁺ then reacts with further dissolved oxygen and the hydroxyl ions (OH^") produced at the cathode to form ferric oxyhydroxide (FeOOH) which is commonly known as rust:

Fe³⁺ + l/2O₂ + OH^" → FeOOH

Under potentially corrosive conditions (eg H⁺ ions in an acidic environment), the exchangeable Ca or other suitable exchangeable metal ion eg. Zn , Al , Mg on the

2+ silica/silicate surface is released into solution as Ca or other respective ions, and at the same time the H ions are captured to the silicate surface:

Bulk-Si-O-Ca → Ca²⁺ + Bulk-Si-O^" + e

Bulk-Si-O^" + H⁺ → Bulk-Si-OH

The released Ca 2+ ions react with the hydroxyl ions produced in the cathodic reaction above to form an impervious microfilm of calcium hydroxide (Ca(OH)₂) at the corrosion site on the metal:

Ca²⁺ + 2OH^" → Ca(OH)₂

Since the reaction:

Bulk-Si-O-Ca → Ca²⁺ + Bulk-Si-O^" + e is anodic, it is effective in inhibiting the corrosion of iron by preventing or reversing the anodic reaction by the cathodic reaction:

Fe³⁺ + 3e →Fe If an anionic metal oxide eg. vanadate, phosphate, manganate is an integral component of a composite metal rich metal oxide silica/silicate product, this anionic metal oxide functions as a chemical passivator in a similar way to that of chromate ions in zinc chromate. The proprietary vanadate, phosphate, or manganate metal oxide component in the composite metal rich metal oxide silica/silicate product does not present the same potential environmental hazard as the chromate ion.

The novel composite metal rich metal oxide silica/silicate products therefore impart corrosion resistance by a combination of mechanisms, which significantly enhance their overall effectiveness in this application.

The Characterisation of the Metal Rich Silica/Silicate and Composite Calcium Carbonate - Calcium Rich Silica/Silicate Products

Structure

The typical microplatelike and microfibrillar structure of the amorphous calcium-rich silica/silicate products are shown by the high resolution electron microscope photos in Figure 2. This product was produced from a water containing 800mg.kg^" SiO₂ and maintained at about 60°C, the dissolved silica of which was precipitated according to the teachings of this patent by adding a slurry of Ca(OH)₂ in an amount to provide lOOOmg.kg^" Ca to the water whilst increasing the pH to 10.8.

This microstructure is significantly different from the Type I, Type II and Type III tertiary structure of the amorphous precipitated silicas described and produced by the teachings of Harper et al. (1990, 1993, 1996, 1997).

Figure 2 shows that the microstructure comprises mainly microfibrils typically about 0.05-0.2 microns (50-200nm) in length and about 0.005-0.01microns (5-10nm) in width which are intertwined to provide a 3D structure. There are also some poorly ordered microplates about 0.02-0.1 microns across and about 0.005 microns thick. In some samples these microplates appear to be rolled up to form the microfibrils. The microplates and microfibrils are intermixed to provide an overall 3D structure with a significant pore structure capable of absorbing up to about 200g oil.lOOg^"1 solid and also a large surface for light scattering. The development of this novel microstructure is therefore fundamental to the development of the excellent oil absorption and light scattering properties inherent in these novel calcium rich silica/silicate products.

Figure 3 shows the microstructure of the composite calcium carbonate - calcium rich silica/silicate product. In this the calcium carbonate microcrystals are typically about

0.1-0.5microns in size and have well defined crystal faces and edges. Some of the microcrystals exist as discrete particles but the majority are encompassed in the microfibrillar and microplate network. In many cases it appears that the actual microfibrils are bonded to the surface of the calcium carbonate particles, presumably by hydrogen bonding between the surface silica silanol groups and the carbonate oxygens.

Again this microstructure imparts the important oil absorption and light scattering properties to the product.

For novel metal rich silica/silicate products where the metal is other than calcium, e.g. Zn ⁺, Cu ⁺, Fe ^{+ +} etc., the material comprises spherical or acicular microparticles which are loosely agglomerated in the solid product.

Oil Absorption. Light Scattering and Surface Area Properties As described above, it has been found that the precipitation conditions for these calcium- rich silica/silicate products, notably the pH and level of added calcium in relation to the dissolved silica content, significantly influence the development of this microstructure and consequently the oil absorption, light scattering and surface area properties of the products. For the above-mentioned product produced from a water containing δOOmg.kg^"1 SiO , maintained at about 60°C, an added calcium content (using a slurry of Ca(OH)₂) of lOOOmg.kg^" Ca and a pH=10.8, the respective values of these properties are:

Oil Absorption (ASTM Spatula Rubout Method 205g oil.1 OOg^"1

D281-31, using Di Octyl Phthalate)

Optical Properties

CIE Scale L*=98.66; a*=-0.06; b*=1.48

ISO Brightness 97.1

TAPPI Brightness 94.5

Surface Area 60m .g^" Furthermore, as noted above, it has been discovered that the development of the microstructure and hence the resulting performance properties can be changed in a controlled manner by varying the pH between values of pH=10-13, the added calcium

9+

(Ca ) content, the dissolved silica (SiO₂) content and the ratio of calcium/silica.

For silica products made from solutions with higher concentrations of dissolved silica e.g. greater than 5,000 mg.kg^" SiO₂, with subsequent pH adjustment of the product slurry or filter cake, the oil absorptions and surface areas of the products can be increased further (see Table la).

The typical range of properties with which products can be produced by this new technology are:

Oil Absorption 100-320g oil.1 OOg^"1

ISO Brightness 91-98

TAPPI Brightness 89-95

Surface Area 50-280m².g^"1 The new technology described here is therefore able, in a simple process, to produce an amorphous precipitated calcium rich silica/silicate material from geothermal water with an oil absorption (205g oil.1 OOg^" ) approaching that of the precipitated reinforced silica product of Harper et al. (1990, 1993, 1996, 1997), (220-230g oil.lOOg^"1) which requires a multistage process. In addition, the ISO and TAPPI Brightness values of the product produced according to the teachings of the new technology exceed slightly those reinforced Type I silica products produced by the technology of Harper et al. (1996, 1997). The surface areas of the calcium rich silica/silicate and reinforced Type I silica products are similar.

Furthermore, as discussed above, the yield of the calcium rich silica/silicate or composite calcium carbonate - calcium rich silica/silicate product produced from geothermal water by the new technology is substantially greater than the Type I, Type II or Type III silica products produced by the Harper et al (1990, 1993, 1996, 1997) technology, from a water source with a particular level of dissolved silica.

The new technology therefore provides substantial process, yield and economic advantages for the production of a silica-containing product with excellent oil absoφtion and optical properties, from geothermal water or water containing dissolved silica.

Typical Examples of Calcium Rich Silica/Silicate and Composite Calcium Carbonate - Calcium Rich Silica/Silicate Products

A typical, but by no means complete suite of examples of these products produced from both natural geothermal waters and synthetic sodium silicate or silicic acid containing solutions, together with their properties and chemical compositions are shown in Tables 1-4. Table 1 - Formation Conditions, Oil Absorption, Surface Area and Optical

Properties of Various Calcium Rich Silica/Silicate and Composite Calcium Carbonate - Calcium Rich Silica/Silicate Products

Table la Formation Conditions of Various Calcium Rich Silica/Silicate Products

Prepared from Solutions With a Higher Dissolved Silica Content and PH Adjustment of the Product Slurry or Filter Cake.

Note 1 : Ca²⁺ added as H - Ca(OH)₂; C - CaCl₂

Note 2: Successive pH values for the same sample reflect the extent of pH adjustment of the amorphous calcium silica/silicate slurry by acid addition. Table lb: Formation Conditions and Properties of Various Composite Calcium Carbonate - Calcium Silica/Silicate Products Precipitated from Kawerau Geothermal Water Using Ca(OH)₂

Table lc: Formation Conditions and Properties of Various Composite Calcium Carbonate - Calcium Silica/Silicate Products Precipitated from Kawerau Geothermal Water Using Ca(OH)₂ with pH adjustment using NaOH

Table 2 - Formation Conditions and Oil Absorption of Various Metal Rich Silica/Silicate and Metal-Anion Silica/Silicate Products

Table 3 - Major Element Oxide Compositions of Various Calcium Rich

Silica/Silicate and Composite Calcium Carbonate - Calcium

Rich Silica/Silicate Products

Note: Samples were analysed by X-ray Fluorescence Spectroscopy using the fused disk method. The compositions are expressed in terms of their major element oxides in accordance with convention. The LOI represents the Loss on Ignition at 1000°C due to the decomposition of CaC0₃ to C0₂ and Hydroxyl groups to water, as well as chemisorbed water. Table 4 - Calcium Carbonate and Chemisorbed Water Content of Various Calcium Rich Silica/Silicate Composite Calcium Carbonate - Calcium Rich Silica/Silicate Products

CaC0₃ and H₂0 content determined by Leco analysis. Table 5 - The Effect of The Amount of Added Ca²* and Consequent pH on the Oil Absorption and Yield of Various Calcium Rich Sϋica/S-licate Products

Water Temperature = 60°C

The "P" series were produced from waters in which the dissolved silica content was provided by adding sodium silicate to the water in the required amount. For this, the waters with 500mg.kg^" SiO₂ represent a geothermal filed of moderate enthalpy e.g. Wairakei, New Zealand; the waters with 800mg.kg^"' SiO₂ represent a geothermal field with a higher enthalpy e.g. Kawerau, New Zealand and Reykjavik, Iceland; and those with lOOOmg.kg^" SiO₂ represent a high enthalpy geothermal field e.g. Mokai and Rotokawa New Zealand. The "W" series were produced from Wairakei geothermal water, the "EF" series from a very low enthalpy field at Empire Farms, Nevada, USA; and the "R", "RA" and "RK" series from the waters of Lake Rotokawa, New Zealand. Products products from Kawerau geothermal water are presented in Tables IB and IC. In the Empire Farms and Lake Rotokawa waters, the dissolved silica content is significantly below that of the silica saturation level at the particular temperature and pH conditions concerned. The recovery of a composite calcium carbonate - calcium rich silica/silicate product from these waters convincingly demonstrates the ability and potential of this new technology to recover such products from low silica-containing waters using the inherent low solubility of the calcium rich silica/silicate phase as the driving force for the recovery process. It is not possible to recover silica from these waters using the method of Harper et al. (1990, 1993, 1996, 1997).

Chemical Composition

Typical major element chemical compositions, determined by major element X-ray Fluorescence analysis and expressed as weight % element oxides are given in Table 2, for the suite of amorphous calcium rich silica/silicate and composite calcium carbonate - calcium rich silica/silicate products. The products prepared from geothermal waters with appreciable quantities of dissolved bicarbonate (EF, R RA and RK) contain appreciable quantities of CaCO₃. The actual CaCO and water contents products have been determined separately by Leco analysis and are presented in Table 4.

APPLICATIONS OF CALCIUM fMETAI RICH SILICA/SILICATE AND COMPOSITE CALCIUM CARBONATE - CALCIUM RICH SILICA/SILICATE PRODUCTS

General The use of a number of novel calcium (metal) rich silica/silicate and composite calcium carbonate - calcium rich silica/silicate products produced according to the teachings of this new technology described here, from a range of natural geothermal waters and synthetic sodium silicate solutions, have been demonstrated in a variety of applications. The applications utilise a single or combination of the properties of the particular calcium (metal) rich silica/silicate material, notably the chemical composition, surface chemical ion exchange, oil absorption, surface area, light scattering and optical properties.

Paper

A number of illustrative examples based on paper will now be given. In its broadest sense "paper" should be interpreted as including 'paper-like' or 'paper-based' materials, including (but not restricted to) cards and boards, shredded paper type products, and as well as including similar fibre based materials. This latter category may include papers including synthetic materials, or including components other than tree cellulose in their manufacture. The techniques described herein are also applicable to most fibre products, and not just paper, and can be considered for such additional luses as is appropriate. Paper Filling: The Use of Calcium Rich Silica/Silicate and the Composite

Calcium Carbonate - Calcium Rich Silica/Silicate Products as a Paper Filler to Reduce Print Through and Increase Opacity and Brightness In the manufacture of paper, various minerals notably clay, calcined clay and calcium carbonate, and to a minor extent synthetic amorphous precipitated silica, are used to reduce print through and enhance the print and optical properties of the paper.

These components may be added as fillers to the paper furnish during the paper forming process in order to increase the opacity and brightness of the unprinted paper, and to enhance print quality and reduce print through in the ensuing printing process. In addition, the components are used extensively in coating formulations which are applied to the paper sheet to provide a coated surface suitable for high quality printing and colour definition.

In order to enhance the opacity and brightness of the sheet and reduce print through, the filler material ideally should have good light scattering properties, a high brightness and a high oil absorption. For paper coating, the material should have good light scattering and high brightness properties. Also for certain coating applications such as for ink jet printing papers, it appears that a high oil (liquid) absoφtion is also desirable.

Calcium carbonate in either the natural ground form (GCC) or the precipitated form (PCC), and also kaolinite clay are widely used in paper filling and coating applications. In general calcium carbonate has a higher brightness than clay, similar light scattering properties, but a lower oil absorption. Calcined clay, which is a thermally modified version of kaolinite clay, generally has increased optical scattering, brightness, and oil absorption properties over those of the filler/coating clay. However, calcined clay is much more abrasive and hence causes significantly more wear on the paper making and paper coating machinery.

Many of the calcium rich silica/silicate and composite calcium carbonate - calcium rich silica/silicate products produced according to the teachings of this new technology and described here (Figures 2 & 3 and Tables 1, 3, 4 and 5), possess the combination of good light scattering, high brightness and excellent oil absorption properties ideally required for paper filling and coating applications.

A number of calcium rich silica/silicate and composite calcium carbonate - calcium rich silica/silicate products products, notably P10, P22, P27, P34, P34, P35, EFP2 and JA2

(Tables 1 , 3 and 4) have been incorporated into paper as a filler and their ability to reduce print through and enhance optical properties of the paper have been evaluated. The results have been compared with that of a reinforced Type I amorphous silica material, which is now recognised as a high performance filler material, effective in enhancing the opacity and reducing print through of newsprint (Harper et al. 1996).

The work has been carried out using standard handsheets made from a typical newsprint paper furnish comprising Kraft and mechanical pulp. To this furnish, sufficient quantities of slurries of each of the above products were added to provide filler levels in the finished paper sheet of about 1 and 3 wt % respectively. The actual silica contents of the sheets were determined by ashing. Appropriate quantities of the P10, P22, P27, P34, P35, EFP2 and JA2 products were each added to the paper furnish to provide a level of filler retained of about 1 and 3 weight % in the sheet. About 50 handsheets for each filler level for each product were prepared and 12 of those in which the basis weight was 48.0±0.5gsm were selected for subsequent print through tests and optical property measurements.

For the print through measurements, samples were prepared and printed according to the PAPRO method 2.404. A suitable strip was cut from the centre of each sheet and the smooth side was printed at 3 inking levels, with 3 test strips per sample, the print through was measured at print densities of 0.85 and 1.00.

In general all the products showed an ability to reduce print through and enhance opacity and brightness. Typical performance values expressed on the basis of percentage improvement per 1 percent of filler in the sheet are given in Table 6 below for a calcium rich silica/silicate product (P27), a composite calcium carbonate - calcium rich silica/silicate product (EFP2) and a calcium rich silica/silicate product prepared with pH adjustment of the slurry (Tables 1 and la). The improvements in print through reduction, opacity and brightness for P27 and EFP2 are similar and compare with those of the PR#5 product of Harper et al. (1996) in the same paper furnish. EFP2 gave slightly increased opacity and brightness. However, JA2 gave a substantial improvement in print through reduction and exceeded that of the amorphous Reinforced Type I precipitated silica of Harper et al. (1996). This is due to the higher oil absoφtion capacity of the JA2 product (Table la). This indeed demonstrates the effectiveness of the products and in particular the JA2 type product as a high performance filler material in paper to reduce print through and enhance optical properties of the paper."

The results demonstrate the effectiveness of these novel calcium rich silica/silicate products, particularly with pH adjustment of the slurry, and composite calcium carbonate - calcium rich silica/silicate products produced by this new technology, in reducing print through and increasing the opacity and brightness of the paper. The enhancement of these three properties is due to a combination of the microstructure of the calcium rich silica and its high oil absoφtion properties, together with the brightness properties of the associated microcrystalline calcium carbonate material.

Table 6 - Typical Performance of calcium Rich Silica/Silicate and Composite Calcium Carbonate - Calcium Rich Silica/Silicate Products as Fillers in Paper

Specialist Papers: The Use of Calcium (Metal) Rich Silica/Silicate and the Composite Calcium Carbonate -Calcium Rich Silica/Silicate Products to Provide the Functional Component in Specialist Papers.

Anti Tarnish Papers

A number of papers containing these novel calcium rich silica/silicate and composite calcium carbonate - calcium rich silica/silicate products as a filler were prepared and their effectiveness as functional wrapping and packaging paper in reducing tarnishing of silverware has been demonstrated.

The tarnishing reaction is invariably caused by the reaction of hydrogen sulfide (H₂S) gas or the bisulfide ion (HS^"), commonly present in volcanic and geothermal areas, and in food (e.g. eggs), reacting with the silver to produce a silver sulfide film on the surface of the silver which is black in colour.

2Ag + H₂S "> Ag₂S

2Ag + 2HS^" "> Ag₂S However, if the silver is wrapped in a paper containing sufficient quantities of novel calcium rich silica/silicate material as a filler, then the calcium (-Si-O-Ca on the surface of the calcium rich silica/silicate material is readily exchanged and reacts with the H₂S gas or the HS^" ion if an aqueous phase is involved, thereby acting as a reactive barrier in "mopping up" the problematic H₂S or HS^" ions.

-Si-O-Ca⁺ + H₂S -> CaS + -Si-OH

-Si-O-Ca⁺ + HS^" > CaS + -Si-OH

In addition, if a tarnished silver surface is cleaned with a moist (tissue) paper containing the novel calcium rich silica/silicate material as a filler, or indeed with a moist paste containing this novel material, the tarnish layer is removed by a combination of mild abrasion and chemical cleaning according to the reaction.

Ag₂S + -Si-0-Ca⁺ + H₂0 > CaS + -Si-OH

Tests showed that when a silver sheet wrapped in a paper containing the calcium rich silica/silicate material (prepared using water containing 800mg.kg^" SiO₂ and precipitated at 60°C using lOOOmg.kg^" Ca ⁺ at a pH=10.8) as a functional filler, and a similar silver sheet wrapped in the same paper which was unfilled, were exposed to an atmosphere of H₂S gas, the silver sheet wrapped in the filled paper remained essentially untarnished, whereas the silver sheet wrapped in the unfilled sheet was considerably tarnished after the same period of time. Furthermore, it has been shown that if a tarnished silver surface is treated with moist paste of these novel products, then some of the tarnish layer is removed chemically and the remainder being removed by very light rubbing.

Anticorrosion Packaging Papers

The chemistry relating to the anticorrosion properties of these novel materials (discussed above) can be utilised to provide novel anticorrosion packaging papers.

A number papers containing these novel calcium rich silica/silicate and composite calcium carbonate - calcium rich silica/silicate products as a filler were made (using for example a product prepared from water containing δOOmg.kg^"1 SiO₂ and precipitated at 60°C using lOOOmg.kg^" Ca ⁺ at a pH=10.8) and their effectiveness as functional wrapping and packaging paper in reducing rusting of steel (iron containing) plates or articles made from steel or iron, evaluated. For this, a steel plate wrapped in the filled paper and a similar steel plate wrapped in an unfilled paper were exposed to a moist environment. After various periods of time the plates were unwrapped and examined. This showed that the steel plate wrapped in the filled paper was essentially free of corrosion, while the steel plate wrapped in the filled paper showed corrosion taking place on the steel surface.

Specialist Filled Papers

The liquid (oil) absorption properties of these novel calcium rich silica/silicate and composite calcium carbonate - calcium rich silica/silicate products using for example a product (prepared for example from water containing 800mg.kg^" SiO₂ and precipitated at 60°C using lOOOmg.kg^" Ca at a pH=10.8) can be utilised to provide specialist filled papers in which a specific functional component e.g. biocide, antiseptic, aromatic flavour etc. is absorbed into the microporous structure of the novel product, and the product is then incorporated as a filler or coating component in the paper. As the dimensions of the pores in the silica products is significantly smaller than that of the pores in the paper, the specific functional component is more tightly held and thereby released over a longer period of time than if the functional component was absorbed directly into the paper pores.

These novel calcium rich silica/silicate and composite calcium carbonate - calcium rich silica/silicate products therefore provide the opportunity to produce specialist papers containing specific functional components which are released slowly over a period of time.

Coated Papers: The Use of Calcium Rich Silica/Silicate and the Composite

Calcium Carbonate - Calcium Rich Silica/Silicate Products as a Functional Component in Paper Coating Formulations.

The combination of excellent brightness, light scattering (opacity) and liquid absoφtion properties of these novel calcium rich silica/silicate and composite calcium carbonate - calcium rich silica/silicate products can also be utilised in paper coating formulations to enhance the brightness and print quality of the printing surface. The precipitated calcium carbonate component in the composite material provides the brightness and opacity typically exhibited by precipitated or very pure ground calcium carbonates, whilst the microstructure of the calcium rich silica/silicate component provides a high oil absoφtion capacity as well as additional light scattering surfaces. A combination of all these properties is usually desirable for a high quality coating surface. In particular, the high oil absorption property offered by this novel material makes it useful in specialist coating formulations for ink jet or non impact printing. A paper coating formulation which may be a size-based formulation incoφorating this novel calcium silica/silicate material with a high oil absoφtion, can be applied to the paper in an off-line coater or at a size press or lick coater in an on-line paper making operation.

In both paper filling and paper coating operations the product(s) may be used directly in slurry form, as a filter cake, or as an appropriately milled powder.

Paint

Anticorrosion Paints: The Use of Metal Rich Silica/Silicate, Metal Rich Metal Oxide

Silica/Silicate and the Composite Calcium Carbonate -Metal Rich Silica/Silicate, Metal Rich Metal Oxide Silica/Silicate Products as Functional Anticorrosion Agents in Paint.

The chemistry relating to the anticorrosion and corrosion protection properties of the metal rich silica silicate and the composite calcium carbonate - metal rich silica/silicate products which involves the exchange of the metal ion from the silica surface, and the metal rich metal oxide silica/silicate and the composite calcium carbonate - metal rich metal oxide silica/silicate products which impart additional passivation protection, has been discussed in detail above.

Anticorrosion and corrosion protection properties have been traditionally imparted to paint formulations by initially incoφorating red lead oxide pigments into the paint. Due to the mounting environmental and health concerns about lead, the paint industry changed to using predominately zinc chromate for this purpose. However, there is currently a similar mounting environmental concern regarding the potential health hazard of the Cr(VI) in zinc chromate. Hence there is an increasing demand in the pigment industry for a functional pigment which is able to impart anticorrosion and corrosion protection properties to a paint film whilst not posing health or environmental problems.

When a number of these novel metal rich silica/silicate and the composite calcium carbonate - metal rich silica/silicate products, and metal rich metal oxide silica/silicate and the composite calcium carbonate - metal rich metal oxide silica/silicate products produced by this new technology are incoφorated into a latex (water-based) or alkyd (oil-based) paint formulation, the anticorrosion and corrosion protection properties inherent in these novel products are imparted to the paint film. In addition, such novel products do not pose the health and environmental concerns of the lead oxide and zinc chromate products.

The anticorrosion and corrosion protection features of these metal rich silica/silicate and the composite calcium carbonate - metal rich silica/silicate products, and metal rich metal oxide silica/silicate and the composite calcium carbonate - metal rich metal oxide silica/silicate products have been tested and evaluated in paint formulations. Such novel products utilising a range of metal cations, and also metal oxide anions have been prepared and added to a standard latex paint which was then applied to the surface of steel test plates. The plates were allowed to weather under normal atmospheric conditions with a marine influence, for periods up to 18 months, and the extent of corrosion of the plates and hence the anticorrosion and corrosion resistance of the paint film evaluated. In addition, the most promising products have been tested in a vinyl etch formulation according to test method AS 1580.452.2 with the results being assessed according to AS 1580.481.3

For this, metal rich silica/silicate and the composite calcium carbonate - metal rich silica/silicate products were prepared from either geothermal water or a solution with a dissolved silica content using a variety of metal cations eg. Zn , Ca , Mg , Al , Cr , Fe and Cu , either as single entities or as double entities in combination eg. Ca /Zn . In addition, composite anion products containing the silica and vanadate or phosphate or chromate or manganate anions precipitated with Ca and/or Zn respectively were prepared. The preparations were carried out at 60°C using water with a dissolved silica content of typically 1000 mg.kg^" SiO₂. The level of added metal cation was typically 200-1000 mg.kg^" and preferably 500 mg.kg^" , and the level of anion typically 200-1000 mg.kg^" and preferably 500 mg.kg^" with the pH generally being adjusted to above pH=10.0. (see Table 2 for detailed conditions). However, higher levels of dissolved silica, added metal ion content and added anion content can be used.

Each product was finely ground and mixed into a standard interior latex paint formulation which had little, if any anticorrosion or corrosion inhibiting properties, or into a specific vinyl etch formulation. At least two coats of each paint were then applied successively to a steel plate in which the edges were masked and sealed. For comparative puφoses, the base latex paint or vinyl etch with no added silica-based products were prepared. Also, two further latex paints were prepared using commercially available replacements for zinc chromate pigment. These comparative paints were similarly applied to steel plates. A cross was scratched through each paint film to expose the underlying metal surface. All samples were placed in the weathering environment and photographed at regular intervals to monitor the corrosion process. At the conclusion of the test, an area of the paint film encompassing part of the scratched cross was removed and the extent of the corrosion on the underlying steel surface evaluated. The thickness of the paint films were also determined.

The results clearly demonstrated the significant anticorrosion and corrosion protection properties of the novel metal rich silica/silicate component or the novel metal rich metal oxide silica/silicate component in the paint formulation. Table 7 presents a comparison of the performance of various metal rich silica/silicate, metal rich metal oxide silica/silicate and the composite calcium carbonate - metal rich silica/silicate, metal rich metal oxide silica/silicate products as anticorrosion and corrosion protection agents in paint.

These results show that the calcium vanadate silica/silicate product imparted excellent corrosion resistant properties to a paint formulation, both in terms of eliminating surface pitting beneath the paint surface and at the bare metal surface (scratch). In addition the results showed that a zinc silica/silicate product offers very good protection against surface pitting and corrosion, and calcium silica silicate product offers good protection against surface pitting and very good corrosion protection to the bare metal. A composite calcium-zinc silica/silicate also offers very good anticorrosion and corrosion protection properties. A similar very good level of protection is provided by a composite zinc silica/silicate-phosphate product. However the corrosion protection of the calcium vanadate silica/silicate product was excellent and it imparted the best overall corrosion protection. Other cations and anions tested provided some corrosion protection properties to the paint film but to a lesser extent than the above zinc, calcium, vanadate and phosphate products.

The novel metal rich silica/silicate and metal rich metal oxide silica/silicate products significantly outperformed the commercial samples 1 and 2. In particular the calcium vanadate silica/silicate product showed a comparable performance to zinc chromate in anticorrosive paint formulations.

It should be noted that the calcium carbonate in the composite products does not provide any anticorrosion or corrosion protection properties to the paint film, but rather acts an an inert filler material.

In summary, the novel calcium vanadate silica/silicate and calcium silica/silicate products in particular, and the zinc rich silica/silicate products, the composite calcium-zinc silica/silicate, the composite calcium phosphate silica/silicate and the zinc vanadate silica/silicate products in general, all impart significant anticorrosion and corrosion protection properties to the paint film, and hence all have significant commercial potential in the paint and coatings industry. The calcium vanadate silica/silicate product is the most effective product overall and can be used as a direct replacement for environmentally problematic zinc chromate in anticorrosive paints.

In a latex paint the product may be used directly in slurry form, as a filter cake or as an appropriately milled powder. However, in an alkyd paint the product must be used in the form of a dried and milled powder. Anti Mould and Anti Fouling Agents

2+

When Cu is used as the metal cation, a copper-rich silica/silicate product is formed using the new technology presented here. In this product the copper is similarly exchangeable and acts as a toxin to mould, fungal and algal growth. Hence this product may be incoφorated into a paint formulation thereby imparting antifouling properties and thus inhibiting or reducing the propensity of mould, fungal or algal growth on the paint surface.

Flatting Agent

In order to reduce the gloss of a surface paint coating and product a matt or flat finish, an inert filler material with an appropriately large particle size is added to the formulation to provide a roughened surface. This disrupts the collective reflectivity of the surface and produces the desired matt effect.

Finely ground or milled quartz (crystalline silica) is often used as this inert filler material. However, there is now some concern with the use of quartz as such fine crystalline materials are deemed to pose a health hazard and may cause silicosis if ingested. Amoφhous, or non crystalline materials such as the novel products described here, are considered not to be a health hazard.

During the formation and slurry handling process, the particle size of the freshly precipitated novel calcium rich silica/silicate and composite calcium carbonate - calcium rich silica/silicate products can be controlled to a certain extent, and can be made to generally conform to the requirements for a flatting agent in paint. It is also possible to control the particle size of a dry product which has been produced by drying a filter cake, in the subsequent milling process.

Table 7 - A comparison of the Anticorrosion and Corrosion Protection Properties of Various Metal Rich Silica/Silicate and the Composite Calcium Carbonate - Metal Rich Silica/Silicate Products.

The flatting properties of novel calcium rich silica/silicate and composite calcium carbonate - calcium rich silica/silicate products in paint films have been evaluated. The samples included the suite of paint films prepared for the above corrosion tests, and a some additional samples. In all cases it was observed that the addition of such novel calcium rich silica/silicate and composite calcium carbonate - calcium rich silica/silicate products to the paint formulation, reduced the gloss level of the paint surface thereby confirming the flatting properties of the product.

The stain and scrub resistance are important properties in a matt paint. In general, high oil absoφtion filler materials produce poor stain and scrub resistance. Hence for this application it is important for the calcium silica/silicate product to have a low oil absoφtion. The preferred products for this application are therefore of the P35, EFP2, and JA2 type (Table 1).

Anticorrosive Agent in Inert Fillers

There are many commercially available inert filler products on the market today which are used in a wide variety of applications. These include filling over steel nails which are punched below the surface of wood, and indentations in steel or aluminium metal panels. The filler formulations usually comprise an inert mineral filler such as clay or calcium carbonate and a binder medium such as a drying oil or an organic polymer. The set filler invariably has some degree of porosity and hence over time moisture can diffuse through the filler to the steel surface and cause corrosion. If such corrosion continues then the filler-metal bond is broken and the filler is exfoliated from the metal surface. As discussed above, the novel metal rich silica/silicate products, particularly where the metal is zinc and/or calcium, possess excellent anticorrosion and corrosion protection properties. The effectiveness of these products in inhibiting such corrosion, when incorporated in inert fillers has been demonstrated. For this, novel zinc and calcium silica/silicate materials were mixed at about a 10% (by weight) level into a commercial inert filler formulation, which was then used to fill holes over punched steel nails penetrating wood, and indentations on steel plates. The inert filler without the added novel product was used to fill a similar set of punched nail holes and steel plates which served as a control. Both sets of wood and metal test beds were placed outside in a natural weathering environment with a marine influence. After about 6 months there were signs of corrosion occurring at the surface of the steel nail heads and the metal indentations on the control samples but not on the samples where the filler contained the novel anticorrosive metal silica/silicate product. Even after 18 months the samples with the anticorrosive product in the filler showed no sign of corrosion whereas in the control sample the corrosion of the underlying nail heads and metal plate was significant. This comparison clearly showed the ability of the novel metal rich silica/silicate products, particularly where the metal is zinc and/or calcium, to provide anticorrosion or corrosion inhibiting properties to such inert filler compounds.

Selective Absorption Applications

The novel microfibrillar and microplatelike structure of the calcium (metal) rich silica/silicate material is responsible for the pore volume and excellent oil absorption of the material, compared with conventional clays, mineral silicates and calcium carbonates. In addition, this microstructure provides a significantly large surface area at which chemical reactions involving silanol groups and fixed or exchangeable metal ions can take place. This combination of novel microstructural and surface chemistry characteristics enables these calcium rich silica/silicate and composite calcium carbonate - calcium rich silica/silicate products to be used in applications where either general broad spectrum absoφtion, or specific absoφtion properties are required.

General Absorption Applications

Examples of general absorption applications, other than in paper and paper printing, may include: Absorbing spills of a wide range of common liquids e.g. oil, other hydrocarbons, wine, beer, alcoholic spirits, fruit juice, cordial and soft drinks, paint etc.;

Absorbing fats and oils in barbecues;

Pet litter to absorb urine and undesirable odours.

The successful use of the novel calcium rich silica/silicate and composite calcium carbonate - calcium rich silica/silicate products all these applications has been demonstrated. Although such uses may be considered low value, they do provide commercial opportunities for off specification products which are occasionally produced in a commercial process.

Specific Absorption Applications. Fruit Preservation - The ability of the novel calcium rich silica/silicate and composite calcium carbonate - calcium rich silica/silicate products to selectively absorb the gases emitted during the ripening of fruit has been demonstrated successfully. It is generally understood that ripening fruit give off ethene (ethylene) gas which in turn catalyses the ripening process for adjacent and less ripe fruit. As the ripening proceeds further to essentially the over ripe stage, carbon dioxide, water vapour, volatile organic acids, alcohols and aldehydes are also evolved. The selective absoφtion of these gases and volatile components provides the opportunity to retard the ripening process and lengthen the shelf or storage life of the fruit.

A series of tests have been carried to determine the ability of these novel calcium rich silica/silicate and composite calcium carbonate - calcium rich silica/silicate products to control and retard the ripening of bananas, apples, nectarines, peaches and pears.

For this, the initial tests were carried out using bananas. Respective pairs of bananas of the same relative ripeness were sealed in plastic bags. Half of the plastic bags also contained a 2g sample of a novel calcium rich silica/silicate or composite calcium carbonate - calcium rich silica/silicate product prepared by rapidly adding lOOOmg.kg^" Ca²⁺ to a solution containing δOOmg.kg^"1 dissolved SiO₂ at 60°C and then filtering and drying the product.

The bags were placed in a typical domestic food storage environment and the extent of ripening monitored and photographed at specific intervals, typically every 3-4 days, over a period of 1 month. As the ripening proceeded with increasing time, it became clear that the bananas sealed in the plastic bags without the novel calcium rich silica/silicate or composite calcium carbonate - calcium rich silica/silicate products, ripened at a faster rate than those which contained the 2g amounts of the novel products in the bags with the bananas.

At the conclusion of the tests the gas given off by the ripening bananas and contained in the respective plastic bags, was sampled and analysed by mass spectrometry. In addition, the novel calcium rich silica/silicate or composite calcium carbonate - calcium rich silica/silicate products in the bag were removed and analysed for their entrapped gas content by mass spectrometry, gas chromatography and for any changes in the silica/silicate structure by infrared spectroscopy.

The results showed that the ethene and carbon dioxide gases, water vapour and volatile organic compounds given off by the ripening fruit were absorbed by the novel calcium rich silica/silicate or composite calcium carbonate - calcium rich silica/silicate product. When this product was then heated, the ethene and volatile organic compounds were largely released. However, much of the water vapour and carbon dioxide were retained in the structure of the calcium rich silica/silicate and composite calcium carbonate - calcium rich silica/silicate product. The infrared spectra suggested the carbon dioxide had reacted with the -Si-O-Ca groups on the surface of the silica/silicate microstructure structure and had formed in situ calcium carbonate. The significant calcium content of the novel product plays an important role here. The water vapour was trapped in the microstructure and presumably hydrogen bonded to the surface silanol groups.

Similar tests were carried out for the apples, nectarines, peaches and pears. Again the tests showed that the ripening of these fruits was slowed by the presence of the novel calcium rich silica/silicate and composite calcium carbonate - calcium rich silica/silicate products, produced according to the new technology presented here. Cigarette Smoke - Cigarette smoke contains a number of chemical constituents that present a health hazard to the smoker and also a number of constituents that impart particular flavours to the inhaled smoke. The selective absorption properties of the calcium (metal) rich silica/silicate and composite calcium carbonate - calcium (metal) rich silica/silicate products can be controlled to some extent by the novel microstructure and the calcium or other metal ions in the product.

The selective absoφtion ability of these different components in cigarette smoke by a suite of these novel products where the metal ion has been calcium, aluminium or magnesium, have been tested successfully. This has demonstrated the ability of these products to selectively absorb such components and hence shows their potential use in this application.

General Carrier Applications

The good liquid (oil) absorption properties of these novel calcium (metal) rich silica/silicate and composite calcium carbonate - calcium (metal) rich silica/silicate products enables them to be used as an inert carrier agent. This application is used when it is desirable to handle, transport or disperse a normally liquid material as a solid, by absorbing the liquid into a highly absorbent and essentially inert carrier host. The novel products with high oil absoφtions, typically greater than about 200g oil.1 OOg^" solid are useful here, and their application in this area demonstrated accordingly. Furthermore, it has been demonstrated that such novel products are useful in absorbing and controlling the subsequent release of fragrances and aromatic liquids, wherein the fragrance or aroma is released at a slower rate over time than is the case for the same quantity of material in its liquid form and exposed to the atmosphere. This is because the propensity for the liquid which is absorbed and held in the microporous structure due to surface tension effects to evaporate and generate the appropriate vapour, is less than that of a free liquid. The net result is that the fragrance or flavour is released more slowly and over a longer period of time.

Hydrophobic Products

It has been determined that when these novel calcium (metal) rich silica/silicate and composite calcium carbonate - calcium (metal) rich silica/silicate products are exposed to the vapour of n-butanol or a similar alcohol in a sealed vessel heated to about 200°C and maintained at the appropriate vapour pressure for 2 hours, the butanol molecule is bonded through the oxygen to the silanol groups on the silica surface. This imparts a hydrophobic nature to the silica surface which renders the material non-wettable and causes the product to float on the surface of the water. Interestingly, the hydrophobic material retains its good oil absoφtion properties, but will not absorb an aqueous phase.

This novel hydrophobic product has the ability to absorb oil from a water-oil mixture or emulsion and hence can be used to selectively the absorb oil spills in a aqueous or marine situation. This property has been convincingly demonstrated whereby a quantity of hydrophobic calcium (metal) rich silica/silicate or a quantity of composite calcium carbonate - calcium (metal) rich silica/silicate product was added and stirred into a water- oil mixture. The oil is readily absorbed by the hydrophobic product and removed from the water-oil mixture. The resulting oil-containing hydrophobic product is usually slightly more dense than water and hence can be readily separated by a conventional settling or filtration process.

These novel hydrophobic calcium (metal) rich silica/silicate and composite calcium carbonate - calcium (metal) rich silica/silicate products therefore provide the unique opportunity to clean up oil spills in an aqueous or marine environment.

Cosmetics and Natural Pharmaceutical Products As discussed above, the excellent liquid absorption properties enables these novel calcium (metal) rich silica/silicate and composite calcium carbonate - calcium (metal) rich silica/silicate products to be used as functional components and inert carriers in cosmetic and pharmaceutical products. This is particularly so for those products derived directly from natural materials where this label can provide a competitive marketing edge. When the product is used in a cosmetic formulation, the liquid absoφtion properties enable undesirable oils and waste products (sweat or perspiration and odours) to be absorbed and removed from the pores of the skin. These can then be replaced by more desirable and beneficial oils and skin treatment products. Also, the calcium content provides a source of calcium for the skin, and if absorbed through the skin pores, into the body itself.

The novel calcium rich silica/silicate and composite calcium carbonate - calcium rich silica/silicate products can be incoφorated in an antiperspirant/deodorant formulation to provide the active absorbing ingredient. Currently the active ingredient in such formulations is typically a chlorohydroxy aluminium material which is raising concern as the aluminium component can be absorbed through the skin and may have an adverse effect on health. In particular there is a concern of the possible link between the aluminium and Alzheimer's disease. The liquid and vapour absoφtion properties of the calcium rich silica/silicate and composite calcium carbonate - calcium rich silica/silicate make it effective in absorbing both body sweat and odours. In addition, the calcium component, if absorbed through the skin provides a beneficial effect, which is in marked contrast to the undesirable effect of aluminium. Various antiperspirant/deodorant formulations have been developed using the calcium rich silica/silicate and composite calcium carbonate - calcium rich silica/silicate as the active ingredient and have been demonstrated successfully.

Some natural composite calcium carbonate - calcium (metal) rich silica/silicate product obtained from the waters of Lake Rotokawa (RA10, RA12, RA13, R21, RK1 and RK4; Table 1) contain about 1 wt % sulfur, which is considered to be a natural antibiotic. In addition, the product contains minor quantities of iron and trace quantities of zinc, copper and phosphorus, which are also considered the be beneficial to health. This composite product from Lake Rotokawa can therefore be used in natural health products and formulations. The composite product can be incoφorated in various lotions, skin preparations and soaps. Examples of these consumer products have been prepared and tested accordingly.

Rubber

For many decades amorphous silicas have been used as reinforcing and property modifying agents in rubber. The products of the present invention may also be incoφorated into rubbers as modifying fillers.

Agriculture and Horticulture Applications

The novel calcium (metal) rich silica/silicate and composite calcium carbonate - calcium (metal) rich silica/silicate products have considerable potential in agriculture and horticulture applications. The high liquid (water) absoφtion and metal ion exchange properties are important here.

When the novel product is mixed with soil or more particularly a potting mix for pot plants, the high liquid absoφtion capacity of the product takes up excess water when the soil is wet and after the soil dries out it releases the water to the plant roots. The use of this product in the soil or potting mix therefore provides the opportunity to be able to regulate the water supply to the plant and extend the period over which water may be made available to the plant under arid conditions.

This application has been demonstrated successfully whereby two closely identical pot plants were selected. The novel product was mixed with the soil of one pot plant and then the soil of both plants were saturated with water. Both plants were allowed to stand in the environment without further watering and their condition monitored regularly. As the soil in the plants dried out the plant potted in the soil containing the novel product continued to flourish whilst the other plant withered and died due to lack of available water. This was repeated a number of times with different plant types. In all cases the plants contained in pots with a mixture of the novel product and soil lasted substantially longer than those potted in soil only. The results therefore clearly demonstrate the effectiveness and use of the novel calcium (metal) rich silica/silicate and composite calcium carbonate - calcium (metal) rich silica/silicate products as water control agents in soil and their ability to lengthen the period between watering and enhance the pot life of plants in arid environments.

In another application, the novel calcium (metal) rich silica/silicate and composite calcium carbonate - calcium (metal) rich silica/silicate products prepared with appropriate amounts of agriculturally or horticulturally important trace elements chemically bonded to the surface silanol groups in the microstructure of the silica/silicate, when mixed with soil are able to provide these trace elements to the plant roots. The elements are released in a controlled manner due to the cation exchange properties of the product as described above. The novel product may be produced from an aqueous solution containing dissolved silica to which appropriate trace metals are added, or alternatively from a natural geothermal water, such as that from Lake Rotokawa with some or many of the trace elements present in the water.

The novel product produced from Lake Rotokawa water has been tested as a fertiliser for a series of plants and the growth of these plants compared with the same series of plants where the novel product was absent from the soil. Over a period of time it was clear that the plants benefited from the use of the novel product as a fertiliser.

Plastics

The novel calcium (metal) rich silica/silicate and composite calcium carbonate - calcium (metal) rich silica/silicate products can be used an inert filler and also as an antiblocking agents in plastics.

References:

Fournier R.O. and Potter R.W. - A Revised and Expanded Silica (Quartz) Geothermometer. Geothermal Resource Council Bulletin, 11, 3-9, 1982.

Fournier R.O. and Rowe J.J. - The Solubility of Amoφhous Silica in Water at High Temperatures and High Pressures. American Mineralogist, 62, 1052-1056, 1977. Harper R.T. - Extraction of Amorphous Silica From Geothermal Water and its Application to Improve Newsprint Quality. Unpublished PhD Thesis, Victoria University of Wellington, 1994.

Haφer R.T., Johnston J.H. and Wiseman N. - The Controlled Precipitation and Use of Amorphous Silica From Geothermal Fluid or Other Aqueous Media Having a Silicic Acid Concentration. New Zealand Patent No. 228472/232170 , 1990.

Haφer R.T., Johnston J.H. and Wiseman N. - Controlled Precipitation of Amoφhous Silica from Geothermal Fluid or Other Aqueous Media Having a Silicic Acid Concentration. US Patent No 5,200,165, 1993. Harper R.T. and Johnston J.H. - The Controlled Precipitation of Amoφhous Silica from Geothermal Fluid or Other Aqueous Media Containing Silicic Acid, Amoφhous Particulate Silica Products Produced Therefrom, and Uses of Such Products. NZ Patent No 245,823, 1996.

Harper R.T., Johnston J.H. and Wiseman N - Controlled Precipitation of Amoφhous Silica from Geothermal Fluid or Other Aqueous Media Having a Silicic Acid Concentration. US Patent No 5,595, 717, 1997.

Her R.K. - The Chemistry of Silica. John Wiley & Sons, Inc., 1979.

Makrides A.C., Turner M. and Slaughter J - Condensation of Silica From Supersaturated Silicic Acid Solutions. Journal Colloid Interface Science, 73, 345-367, 1980. Marsh A.R., Klein G. and Vermeulen T - Polymerisation Kinetics and Equilibria of Silicic Acid in Aqueous Systems. Report No. LBL-4415, under contract ERDA W-7405- ENG-48, University of California, Berkley, October 1975.

Rothbaum H.P. and Anderton B.H. - Removal of Silica and Arsenic from Geothermal discharge Waters by Precipitation of Useful Calcium Silicates. Proceedings 2nd United Nations Symposium on the Development and Use of Geothermal resources, San Francisco, 1417-1425, 1975.

Rothbaum H.P. and Rhode A.G: Kinetics of Silica Polymerisation and Deposition From Dilute Solutions Between 5 and 180°C. Journal Colloid Interface Science, 71, 533-559, 1979. Weres O., Yee A. and Tsao L. - Kinetics of Polymerisation. Lawrence Berkley Laboratory Report No. 7033 UC-4, 1980.

Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the spirit or scope thereof as defined in the appended claims.

Claims

THE CLAIMS DEFINING THE INVENTION ARE:

1 . A method of forming desired silica products in an aqueous system containing at least one dissolved member of a preferred group of reactant silica components comprising: silica, silicic acid, silicate ions, and silicilate ions; and wherein said method comprises the reaction of reactant silica components in the aqueous system with at least one metal ion reactive therewith; and wherein the reaction conditions are adjusted or maintained such that the formation of desired silica products, as herein defined, substantially occur above a pH of 9.5.

2. A method as claimed in claim 1 which is performed according to the steps of: i) should the pH of the aqueous system be below 9.5, increasing the pH of the aqueous system above 9.5 prior to any substantial polymerisation of preferred reactant silica components, and subsequently ii) introducing to the aqueous system at least one metal ion reactive with one or more reactant silica components present in the aqueous system.

3. A method as claimed in claim 1 which is performed according to the steps of: i) introducing to the aqueous system at least one metal ion reactive with one or more reactant silica components present in the aqueous system, said introduced metal ion being in the form of an alkaline compound such that should the pH of the aqueous system be below 9.5, the pH of the aqueous system is raised above 9.5; the consequential increase in pH to above 9.5 being effected prior to any substantial polymerisation of preferred reactant silica components.

4. A method as claimed in claim 3 in which the pH of the introduced metal ion portion is adjusted with acid or alkali to a pH such that when the desired amount is introduced to the aqueous system, the resulting pH is within the range of 11.0 through 13.9 inclusive.

5. A method as claimed in any one of the preceding claims which includes an additional step subsequent to reaction between said components, said step comprising lowering the pH to within the pH range of 7 through 10 inclusive.

6. A method as claimed in either claim 4 or claim 5 in which the concentration of reactant silica components is a silica (SiO₂) concentration within the range of 5000 through

20,000 mgkg^-1 inclusive.

7. A method as claimed in any one of claims 1 through 6 in which the pH is raised to 10 or above for the formation of desired silica products.

8. A method as claimed in any one of claims 1 through 7 in which the aqueous system comprises substantially geothermal water.

9. A method as claimed in claim 8 which includes an extraction step for removing insoluble product, said extraction step being performed when the aqueous system has been cooled to a temperature within the range of 15 through 100°C inclusive.

10. A method as claimed in either claim 8 or claim 9 in which, after reaction of the components the level of dissolved preferred reactant components remaining in solution is less than 50mg.kg^" .

1 1. A method as claimed in any one of claims 1 through 8 in which raising of pH is at least partially accomplished by adding an alkaline material not directly participating in the reaction forming the desired silica products.

12. A method as claimed in claim 11 in which the alkaline material is a hydroxide of an alkali metal.

13. A method as claimed in any one of claims 1 through 8 in which, if the pH is raised to a pH exceeding 13, there is a subsequent downward pH adjustment after component reaction to a pH within the range of 7 through 10 inclusive.

14. A method as claimed in any one of claims 1 through 8 in which the resulting insoluble products of reaction are substantially free of Type I, II, or III silica products as defined in patents US5200165 or US5595717.

15. A method as claimed in any one of claims 1 through 8 in which in which increase of the pH of the aqueous system is performed before more than 25% (by weight) of the dissolved preferred reactant silica components have polymerised.

16. A method as claimed in any one of claims 1 through 8 in which an introduced metal ion is of an element having a silicate or silica product of lower aqueous solubility than the preferred reactant silica component with which the metal ion reacts.

17. A method as claimed in claim 16 in which an introduced metal ion is a cation of one of the following elements: Ca, Mg, Al, first row transition metals, Mo, Sn, Cd, Pb, Ba, and second row transition metals.

18. A method as claimed in claim 16 in which the introduced metal ion is introduced as an oxide or hydroxide of Ca.

19. A method as claimed in claim 16 in which the introduced metal ion is introduced as an oxide or hydroxide of Mg.

20. A method as claimed in claim 16 in which an introduced metal ion is introduced in the form of a soluble salt of the element.

21. A method as claimed in any one of claims 1 through 8 in which insoluble products are removed from the aqueous system and the remaining supernatant solution is recycled; additional preferred reactant silica components being introduced into solution prior to a repetition of their repeated reaction with introduced metal ions.

22. A method as claimed in any one of claims 1 through 8 in which after introduction of the introduced metal ion, the system is allowed to stand for a period allowing the desired products to form and precipitate, and optionally increase in average particle size.

23. A method as claimed in any one of claims 1 through 8, performed in a manner whereby the desired silica products comprise components having either or both of a microfibrillar and microplatelike structure, as hereindescribed.

24. A method as claimed in any one of claims 1 through 8, performed in a manner in which the resulting desired silica products comprise components having an oil absoφtion value exceeding lOOg.oil per lOOg silica product.

25. A method as claimed in claim 24 in which oil absoφtion in the product is controlled by altering pH and the level of added metal ion.

26 A method as claimed in any one of claims 1 through 8 in which the proportion of introduced metal ion is within the range of 1: 1 to 1.4: 1 inclusive of silica to metal measured as a weight ratio, and the pH is maintained within the range of 10.3 to 11.6.

27. A method as claimed in any one of claims 1 through 8 in which the proportion of introduced metal ion is within the range of 1.1: 1 to 1.25:1 inclusive of silica to metal measured as a weight ratio.

28. A method as claimed in any one of claims 1 through 8 in which is also introduced, in addition to metal cations, anions including metallic elements.

29. A method as claimed in claim 28 in which the metal of the metallic anion is a different element from the introduced metal cation.

30. A method as claimed in claim 28 in which the metal of the metallic anion comprises: Zn,

Cr, V, Mo, Ni, Ti, Sn, Fe, Cu, Al, Mn, or Co.

31. A method as claimed in any one of claims 28 through 30 in which anions of more than one metallic element are introduced.

32. A method as claimed in any one of claims 1 through 8 in which there is present, in the aqueous system, dissolved reactant carbonate components and wherein an introduced metal cation is reactive to these components to form a substantially insoluble product; the amount of introduced metal cation being sufficient to cater for both the reaction with preferred reactant silica components and dissolved reactant carbonate components.

33. A method for removing dissolved silica from geothermal waters, or non-geothermal artificial systems with dissolved silica, to a level of less than lOOmg.kg^" of water, said method comprising the conversion of dissolved reactant silica components to a low solubility silica compound of a metal at a pH exceeding 9.5, and removing the precipitated product.

34. A silica product resulting from a method according to any one of the preceding claims.

35. A silica product which is a desired silica product as defined herein and is characterised by substantially comprising particles which are either or both platelike, or microfibrillar, in character.

36. A silica product which is a desired silica product as defined herein and is characterised by having an oil absoφtion capacity of lOOg oil.1 OOg^" silica or greater.

37. The silica product of either claim 35 or claim 36 when produced according to a method as claimed in any one of claims 1 through 29.

38. A silica product, as claimed in any one of claims 34 through 37 which includes a proportion of either or both a carbonate, or hydrogen carbonate compound.

39. A silica product as claimed in claim 38 in which a proportion of the carbonate or hydrogen carbonate compounds are at least partially encapsulated or incoφorated into the structures of the precipitated silica products.

40. A silica product, as claimed in any one of claims 34 through 39 in which the predominant metal ion present is calcium.

41. A silica product, as claimed in any one of claims 34 through 39 which has an oil absoφtion capacity of 200g oil.lOOg^" silica or greater, and comprises a system in which the introduced metal cation is between 1 - 1.4 times the amount (by weight) of dissolved reactant silica components.

42. A silica product, as claimed in any one of claims 34 through 39 when used for increasing the opacity of paper or film products.

43. A silica product, as claimed in any one of claims 34 through 39 when used for reducing print-through in paper products.

44. A silica product, as claimed in any one of claims 34 through 39 in a coating formulation applied to paper to enhance either or both print quality and surface finish.

45. A silica product, as claimed in any one of claims 34 through 39 when used for modifying the physical characteristics of paper or film products.

46. A paper or film product including a silica product as claimed in any one of claims 34 through 39.

47. A paper of film product as claimed in claim 46 having anti-tarnish properties.

48. A silica product, as claimed in any one of claims 34 through 39 for use in anti-mould and or anti-fouling applications, and in which an introduced metal cation was copper.

49. An anti-mould and/or anti-fouling paint or coating incoφorating a copper containing silica product as claimed in claim 48.

50. A silica product, as claimed in any one of claims 34 through 39 when used as an absoφtive agent for liquids or gases.

51. A silica product, as claimed in claim 50 whose preparation was optimised for absoφtion of ethylene.

52. An absoφtive desired silica product, as claimed in either claim 50 or claim 51, which is used to control the ripening of fruit.

53. A packaging element or film incoφorating an absoφtive desired silica product as claimed in either claim 50 or claim 51 and in which the ethylene absoφtive silica product is held or presented in a manner such that it is accessible to gaseous ethylene or other gases influencing ripening, present in the environment with which it is intended to interact.

54. A method for preventing the early ripening of fruit comprising introducing an accessible absoφtive silica product as claimed in claim 53 into the environment of the fruit.

55. A silica anion product produced according to a method as claimed in any one of claims 1 through 33 which comprises an anion-silicate type compound of a metallic element, the ratios of the anion, silicate and metallic element portions not necessarily being stoichiometrically consistent, and wherein the silicate portion may include silicates, silicilates, and other predominantly silicon-oxygen moieties.

56. A silica anion product as claimed in claim 55, in which the anion includes a metallic or semi-metallic element.

57. A silica anion product as claimed in claim 56 which includes at least one of: phosphorus, zinc, aluminium, vanadium, chromium, manganese, molybdenum, copper, aluminium, or cobalt.

58. A silica anion product as claimed in claim 56 which includes a transition metal element.

59. A silica anion product as claimed in any one of claims 56 through 58 in which the anion comprises the metallic or semi-metallic element in combination with oxygen.

60. A silica anion product as in any one of claims 56 through 58 in which an anion incoφorating a metallic or semi-metallic element was introduced during its preparation.

61. A silica anion product as in any one of claims 56 through 58 in which the introduced anion was at least one member of a group comprising: a member of the phosphate group, a vanadate, a molybdate, a permanganate, a manganate, a member of the chromate group, or a cobaltate.

62. A silica anion product as claimed in any one of claims 56 through 61 for use as an anticorrosive agent for ferrous metals.

63. An anticorrosive paint or coating product incoφorating a silica anion product as claimed in any one of claims 56 through 61.

64. An anticorrosive paint or coating product incoφorating a silica product as claimed in any one of claims 34 through 39.

65. An anticorrosive fibre product incoφorating a silica product as claimed in any one of claims 34 through 39.

66. An anticorrosive fibre product as claimed in claim 65 which is a paper based product.

67. The anticorrosive fibre product of claim 65 or claim 66 when used for wrapping or separating metal or metal coated articles.

68. A method for protecting ferrous metals comprising the deposition of either or both a silica anion product as claimed in any one of claims 56 through 61, or a desired silica product as claimed in any one of claims 34 through 39, on to a surface of said metal.

69. A silica product, as claimed in any one of claims 34 through 39, which has been modified to exhibit hydrophobic properties.

70. A hydrophobic silica product, as claimed in claim 69, in which the silica product has been reacted with a C₄ or greater alkyl alcohol.

71. A silica product, as claimed in any one of claims 34 through 39, when added to rubber to alter its physical properties.

72. A silica product, as claimed in any one of claims 34 through 39, when used in pet litter products.

73. A silica product, as claimed in any one of claims 34 through 39, when used as a filtering, adsoφtive, or absoφtive agent for non-particulate matter in fluids and/or gases.

74. A silica product, as claimed in any one of claims 34 through 39, when used as a filtering agent for particulate matter in fluids and/or gases.

75. A silica product, as claimed in any one of claims 34 through 39, when used as a selective absorbent or filtering agent in cigarettes.

76. A silica product, as claimed in any one of claims 34 through 39, when used to selectively absorb oils or a hydrophobic liquid in the presence of water or another hydrophilic liquid.

77. A silica product, as claimed in any one of claims 34 through 39, when used in cosmetic formulations and products.

78. A silica product, as claimed in any one of claims 34 through 39, when used in natural pharmaceutical formulations and products.

79. A silica product, as claimed in any one of claims 34 through 39, when used as a moisture control agent in soils and potting mixes.

80. A silica product, as claimed in any one of claims 34 through 39, when used as an antiblocking agent and/or filler in plastics. A method of forming a desired silica product in an aqueous system containing at least one dissolved member of a preferred group of reactant silica components comprising: silica, silicic acid, silicate ions, and silicilate ions; the concentration of such being such that the pH of the system exceeds pH 11 , and wherein said method comprises the reaction of reactant silica components in the aqueous system with at least one metal ion reactive therewith; the metal ion being in the form of an alkaline compound, or in combination with an alkaline compound, such that at the completion of the reaction with the reactant silica components the pH exceeds 12, and wherein subsequently the pH of the system is reduced to within the range of pH 7 through 10 inclusive.