AU674091C - Kaolin derivatives - Google Patents

Description

KAOLIN DERIVATIVES

THIS INVENTION relates to derivatives of kaolin group minerals and is particularly concerned with such derivatives which have high specific surfaces and/or high cation exchange capacities.

The kaolin group minerals comprise kaolinite, nacrite, dickite and halloysite, and are among the most common clay minerals in nature. They have a 1:1 layered structure, that is, each layer consists of one tetrahedral silicate sheet and one octahedral sheet, with two-thirds of the octahedral sites occupied by aluminium. Kaolinite, nacrite and dickite all have the ideal chemical composition: Al₂Si₂0₅(OH)₄ They differ from one another only in the manner in which the 1:1 layers are stacked. Halloysite, in its fully hydrated form, has the ideal chemical composition:

Al₂Si₂0₅(OH)₄.2H₂0 and differs from the other three members of the group by including molecular water in the interlayer.

Of the kaolin group minerals, kaolinite is the most abundant and has received most attention in terms of its structure, properties and industrial applications. However, because of its close similarity with the aforementioned polytypes, many of the properties and uses described for kaolinite apply equally to the other polytypes. Consequently, for the purposes of expediency, the following disclosure will be restricted primarily to kaolinite and halloysite but it should be borne in mind, as it will be readily appreciated by those skilled in the art, that the invention applies equally to nacrite and dickite.

Naturally occurring kaolins typically have a wide range of particle sizes, particle crystallinity, minor element compositions) and chemical reactivity for intercalation reactions. Kaolins sorted into a size range of 0.5 - 2.0 mm typically have a specific surface of about 5 m²g^_1 and a cation exchange capacity of 10 meq./lOO gm or less. These, and other properties, such as opacity and rheology, make kaolins suitable for a wide range of uses including paper coatings and fillers, pottery, porcelain and sanitaryware production and fillers in paints and rubbers. These properties do not allow kaolins to be readily utilised as catalysts, carriers, absorbents and so on. However, if their specific surface could be increased, their usefulness would be increased even further and they may be used in many other applications including use as catalysts, metal scavengers, carriers, absorbents and so on. In view of this, there has been considerable and ongoing interest in finding a process for delaminating the layered kaolin structure as such delaminated structures have the potential of making available for reaction large surface areas between the layers. To date, delamination has not been demonstrated despite substantial research on the intercalation of kaolinite and its polytypes. Recent research by N. Lahav [(1990), Clays and Clay Minerals 38, 219-222)] suggested a stable suspension of delaminated kaolinite which had been treated with dimethylsulfoxide and ammonium fluoride in aqueous solution. The result was inferred on the basis of change of particle size and there was no evidence of the independent existence of the kaolinite reaction product.

It is therefore an object of the present invention to provide derivatives of the kaolin group minerals which are at least partially delaminated and, as a consequence, have higher specific surfaces than the kaolin group minerals per se.

According to one aspect of the present invention, there is provided a process for the preparation of a Kaolin Amorphous Derivative (KAD), which process comprises reacting a kaolin group mineral with an aqueous alkali halide, wherein the mole ratio of alkali metal halide (MX) to the kaolin group mineral (Al₂Si₂0₅(OH)₄) is from 5 to the saturation concentration of the alkali metal halide. This process need not be restricted to a homogeneous, single-phase kaolin, in that the kaolin, which may contain impurity phases such as anatase, ilmenite, geothite, quartz or cristobalite, when processed in a similar manner may also result in a material comprising predominantly a KAD.

Kaolins may deviate significantly from the ideal stoichiometry as noted above, for example by containing up to 2 weight percent Fe-oxide. This process for formation of a Kaolin Amorphous Derivative is also applicable to kaolins which contain significant amounts of cations, such as Fe ⁺ or Fe ⁺, within the structure or on the surface of individual crystals. The preferred mole ratio of alkali metal halide to kaolin is in the range of 15 to 25.

Another aspect of the invention concerns the Kaolin Amorphous Derivative per se.

Reaction is suitably carried out at an elevated temperature for a sufficient period of time to enable conversion to the Kaolin Amorphous Derivative. Standard pressure conditions are satisfactory for the conversion reaction. However, the transformation of a compound with a predominantly octahedrally-coordinated aluminium to an amorphous derivative with predominantly tetrahedrally-coordinated aluminium may occur by a suitable combination of temperature, pressure and time of reaction given the appropriate reactants. For example, it is within the broad scope of claims of this invention that KAD may be formed from a kaolin by reacting with an alkali halide at temperatures up to 150°C. Alternatively, a kaolin and alkali halide may be reacted for shorter periods of time at elevated pressures (up to lkbar) and higher temperatures (up to 300°C) to form an amorphous derivative.

Preferably, the kaolin is reacted by completely dispersing it in the aqueous alkali metal halide solution and heating the dispersion to a temperature between 70°C and 150°C at atmospheric pressure for a period of between 1 minute and 100 hours until complete conversion has occurred. The excess alkali metal halide is then removed from the reaction mixture by rinsing with water until no halide can be detected in the elute. The resultant solid contains a mixture of KAD and relatively insoluble halide byproducts. The halide byproducts are removed by rinsing the solid mixture with alkali hydroxide to leave substantially pure Kaolin Amorphous Derivative.

The reaction conditions are such that only partial modification of the individual kaolin layers occurs without their complete disintegration or dissolution. The inner surfaces of some of the "layers" remain exposed following the chemical modification resulting in a substantial increase in specific surface compared with unreacted kaolin.

The dried Kaolin Amorphous Derivative prepared by this procedure is a white powder having a specific surface of between 45 m g^"1 and 400 m²g^-1, i.e. manyfold that of the starting material. A typical chemical composition of this Kaolin Amorphous Derivative, as determined by a combination of energy dispersive X-ray spectroscopy in the scanning election microscope, wet chemical analysis and electron microprobe, is:

^.l^A11.33^Si2^O5.5<^O >2.0^F0.1^#1-^9H2°

The composition of Kaolin Amorphous Derivative depends on the composition of the starting materials, whether the reaction has gone to completion (i.e. how much kaolin starting material remains) and to what extent reaction byproducts have been removed by rinsing with water and alkali hydroxide. If we assume that no mineral impurities, as mentioned above, are present and that the reaction product has been thoroughly rinsed, then the composition of Kaolin Amorphous Derivative will normally fall within the following range: pAI qSi 2,0 r(^λOH) ' βX t»uH, 20 where M is an alkali metal cation, X is a halide, 0.5 < p < 2.0, 1.0 ≤ q ≤ 2.2, 4.5 ≤ r ≤ 8.0, 1.0 ≤ s < 3.0, 0.0 < t -≤ 1.0 and 0.0 < u < 3.0.

The structure and morphology of the Kaolin

Amorphous Derivative has been analysed by NMR (nuclear magnetic resonance), XRD (X-ray diffraction), SEM (scanning electron microscopy), and TEM (transmission electron microscopy). Solid state NMR is able to provide information on the local chemical environment of the magnetic nuclei. In particular, Al NMR is sensitive to the co-ordination environment, that is, whether the atom is 4, 5 or 6-coordinated, whereas, for framework aluminosilicates Si NMR can also give information about the number and occupation of neighbouring tetrahedral sites, e.g. it can resolve Si(nAl) n = 0-4.

The Al MAS NMR spectrum for KAD gives a dominant peak centred on "55 ppm (F HM ~ 16 ppm) (see Figure lb), which is interpreted as tetrahedrally coordinated Al. This is in contrast to the ²⁷A1 MAS NMR spectrum for kaolinite which gives a single resonance at "0 ppm (FWHM ~ 20 ppm), which corresponds to octahedrally coordinated Al. The ²⁹Si MAS NMR spectrum of KAD consists of a broad (FWHM ~ 13 ppm) signal centered on -86 ppm (see Figure 2b). This compares with the very narrow signal observed for kaolinite centred on -91.5 ppm (FWHM ~ 1.4 ppm). Apart from the broadening of this peak, which would be expected as a result of the breakdown of the layered structure, the average chemical environment is approximately the same as in the kaolinite starting material.

KAD is XRD-a orphous, that is, it does not show any substantial long-range structural ordering. The XRD profile for KAD consists typically of a broad hump between 14° and 40° 2q for CuKa radiation. No diffraction peaks are observed except for those belonging to impurity phases such as anatase or quartz, which may come from the kaolin starting material. If KAD is not thoroughly rinsed with water and then an alkali hydroxide solution, minor levels of reaction byproductsare difficult to avoid completely. If the alkali halide is RbX or CsX, a broad diffraction peak occurs at the centre of the broad hump attributable to KAD in an XRD pattern.

High magnification scanning electron microscopy, and transmission electron microscopy both show that KAD consists of aggregates of very small anhedral particles of approximate dimensions <50nm. Figures 3a and 3b show TEM micrographs of the typical kaolinite grains before reaction and reacted KAD product, respectively. Note the significant change in morphology from large, micrometre-sized hexagonal plates of kaolinite (Figure 3a) to anhedral nanometre-sized (~40nm) particles which have aggregated into large clumps ("1 m) in size). Figures 4a and 4b show TEM micrographs for typical tubular halloysite grains and the reacted KAD product from this starting material, respectively. As disclosed above, the Kaolin Amorphous Derivative has the chemical composition: M_pAl_qSi₂0_r(0H).X_t.uH₂0 where M is an alkali metal cation, X is a halide, 0.5 < p ≤ 2.0, 1.0 ≤ q ≤ 2.2, 4.5 ≤ r < 8.0, 1.0 ≤ s ≤ 3.0, 0.0 ≤ t ≤ 1.0 and 0.0 ≤ u ≤ 3.0. In one specific form, the as-prepared Kaolin Amorphous Derivative contains the element potassium, such that M=K. In this and subsequent terminology, the acronym "KAD", by default, refers to the potassium-containing Kaolin Amorphous Derivative.

In this material it is possible to exchange, at least partly, the alkali metal cation with any cation which is stable in aqueous solution. Such exchange cations include other alkali metal cations, alkaline earth cations, transition metal cations, lanthanide and actinide cations, heavy metal cations and ammonium. While exchange does not proceed to completion for all cations, there are many transition metal cations (e.g. Mn ^*, Cr ^*, Co^*, Ni ^*, Cu ^*, Zn ^*, Ag^*), lanthanide cations (e.g. La ^*, Nd³⁺) and heavy metal cations (e.g. Pb^2*, Cd^2*, Hg ^*) which do. For some cations exchange is complete after 3 hours at room temperature (e.g. Pb 2+, Cu 2*) ., while others require longer times and temperatures up to 110°C (e.g. Zn^*). The terminology used for this type of amorphous derivative which has undergone an exchange reaction includes the dominant element after exchange (e.g. M-KAD where M=Cu or M=Pb, as indicated in the text below).

Such cation exchange essentially preserves the XRD-amorphous character of the unexchanged KAD as described above. However, the specific surface of the exchanged materials, while still manyfold that of kaolin, does increase or decrease depending on the exchange cation. Examples of this are given in Table 1.

TABLE 1 Comparison of Surface Areas for some Metal-Exchanged KADs

The rate at which this cation exchange occurs can be changed by the application of chemical techniques used by those skilled in the art. For example, as shown in Figure 5, the rate of exchange of Pb ^* with K^* is increased at a temperature of 50°C compared to exchange at room temperature. In addition, this exchange reaction can be reversed on suitable treatment of the exchanged KAD (e.g. Cu-KAD). An example of such treatment on a Cu-exchanged KAD is the use of ammonia solution to generate a soluble ammine complex. In this exchange, NH₄ ^* replaces the Cu ^* cations. This property has particular use in the recovery of transition metals or other cations which have been removed from solution or from a slurry by KAD.

The substantially increased specific surface makes the Kaolin Amorphous Derivative a useful replacement for conventional catalysts such as those used in the rearrangement and conversion of hydrocarbons, as well as for novel applications in this regard.

Another application is the loading of lanthanides and/or transition metals on the Kaolin Amorphous Derivative in reduction-oxidation catalysed reactions. An example of this is the dehydrogenation of methanol to give methyl formate.

Many other applications will be apparent to the skilled addressee.

Specific examples of the synthesis of KAD from naturally occurring kaolins as well as cation exchange and catalysis reactions follow.

EXAMPLE 1 Preparation of KAD from Kaolinite

1.0 g of kaolinite obtained from Weipa, Queensland, Australia, and 4.5 g of potassium fluoride are thoroughly mixed with 2.0 ml of water. The mixture is heated in an oven at 100^βC for 2.5 hours. The reaction products are then dispersed in 100 ml of distilled water and centrifuged until the solid fraction has completely settled. The elute containing the excess salt and a small amount of the weakly soluble fluoride byproducts is decanted. This rinsing process is repeated until no further fluoride can be detected in the elute by the addition of silver nitrate solution, typically 3 to 4 rinses. The remaining solid is dried at 110^βC in air and comprises a mixture of KAD and relatively insoluble fluoride byproducts as shown by XRD (see Figure 6b). The combined weight of the mixture is 1.19 g. The flouride byproducts are removed by dispersing the solid mixture in 40 ml of 0.02 M potassium hydroxide solution (pH = 13) for 30 minutes at room temperature. The suspension is then centrifuged until the solid fraction has completely settled. The alkaline elute containing the dissolved fluoride byproducts is decanted. The remaining solid is now rinsed with cold water until the pH of the elute drops to 8. The solid is dried at 110^βC to give a final yield of 0.95 g and comprises KAD together with the minor impurity mineral anatase, as evidenced by XRD (see Figure 6c). Figure 6a shows an XRD trace for kaolinite before reaction to KAD. The BET surface area measurement for this KAD, after pre-treatment at 110°C for four hours, is 100(1) m2g^~ .

Bulk compositional analyses have been obtained from a suitably prepared pressed disk of the KAD powder prepared from kaolinite, as well as of the same KAD powder after heating to 650°C, using an electron microprobe and are summarised in Table 2. In this table, the values in parentheses are estimated standard deviations to the last significant figure for the weight percentage oxides calculated according to conventional statistical methods.

Table 2*

Composition of KAD prepared from Weipa kaolinite

all values are we ght percentages

Example 2. Preparation of KAD from Halloysite 10.0 g of halloysite obtained from Mataura Bay, Northland, New Zealand, and 42.0 g of potassium fluoride are thoroughly mixed with 20.0 ml of water. The mixture is heated in an oven at 95^βC for 1.0 hour. The reaction products are then dispersed in 1 litre of distilled water and the solids allowed to settle for 2 hours. The elute containing the excess salt and a small amount of the weakly soluble fluoride byproducts is decanted. This rinsing process is repeated until no further fluoride can be detected in the elute by the addition of silver nitrate solution, typically 5 rinses. After the final rinsing the slurry is centrifuged until the solid fraction has completely settled. The remaining solid is dried at 110^βC in air and comprises a mixture of KAD and relatively insoluble fluoride byproducts with a combined weight of 13.9 g as shown by XRD (see Figure 7b).

The flouride byproducts are removed by dispersing the solid mixture in 400 ml of 0.02 M potassium hydroxide solution (pH = 13) for 30 minutes at room temperature. The suspension is then centrifuged until the solid fraction has completely settled. The alkaline elute containing the dissolved fluoride byproducts is decanted. The remaining solid is now rinsed with cold water until the pH of the elute drops to 8. The solid is dried at 110^βC to give a final yield of 9.7 g and comprises KAD together with the minor impurity minerals quartz and cristobalite, as evidenced by XRD (see Figure 7c). Figure 7a shows an XRD trace of the halloysite before reaction to the amorphous derivative.

The BET surface area measurement for this KAD, after pre-treatment at 110°C for four hours, is 167(1) m²g^_1.

Bulk compositional analyses have been obtained from a suitably prepared pressed disk of the KAD powder prepared from the halloysite, as well as of the same KAD powder after heating to 650°C, using an electron microprobe and are summarised in Table 3. In this table, the values in parentheses are estimated standard deviations to the last significant figure for the weight percentage oxides calculated according to conventional statistical methods.

Table 3*

Composition of KAD prepared from Mataura Bay tubular halloysite

*all values are we gh percentages.

In aqueous suspension, M-KAD (M = alkali metal or ammonium cation) has a particular affinity to certain other cations. The cations include the alkaline earths Mg^2*, Ca^2* and Sr^2*, the transition metals Cr^3*, Mn^2*, Co^2*, Fe^2*, Ni^2*, Cu^2*, Zn^2*, Ag^*, Cd^2*, and Hg^2*, as well as Pb^2*, the lanthanide Nd ,3+, and the actinide UO 2* Due to the similar chemical behaviour of trivalent lanthanides it is assumed that the properties demonstrated for Nd^3* apply to all trivalent lanthanides, including Y^3* . The affinity of KAD for these cations has been demonstrated by measuring the percent uptake of each of these cations from a solution containing a low concentration (10-100 ppm) of the subject cation and a relatively high concentration of Na^* (0.1 M). The details of these experiments together with their results are given n Example 10.

The level of selectivity of M-KAD towards these cations is relatively independent of temperature but the rate of exchange is significantly enhanced by increase in temperature. This increase in exchange rate is shown by the example below.

Example 3 Kinetics of Cu 2* Exchange

0.25 g of KAD was dispersed in 100 ml of 0.1 M NaN0₃ solution containing 100 ppm Cu^2*. The KAD was stirred throughout the experiment and aliquots of the solution were removed as a function of time. The aliquot was immediately centrifuged to remove suspended KAD and the solution analysed for remaining Cu ^*. The % Cu^2* removal as a function of time at room-temperature (20^βC) and at 50^βC is given in Table 4 below.

Table 4

Percentage Cu 2* Removed from Standard Solution

EXAMPLE 4 Kinetics of Pb^2* Exchange

0.25 g of KAD is thoroughly dispersed in 100 ml of a 0.1 M solution of NaN0₃ which contains 100 ppm of Pb^2*. The suspension is stirred for 3 hours at room-temperature then centrifuged. Atomic absorption spectroscopic (AAS) analysis of the elute showed that the KAD-treated solution contained only 1 ppm of Pb ^* that is, there had been a 99% reduction in the Pb ^* concentration of the Na^*-rich solution. A plot of this exchange reaction, for data obtained at three different solution temperatures is given in Figure 5.

The level of selectivity of KAD towards these various cations is essentially retained across a wide range of pH conditions. Of particular importance is the stability and the preservation of selectivity of KAD at low pH as it is under these acid conditions that most of the cations mentioned above are most soluble. This property is particularly relevant for the application of KAD in sequestering and retrieving these cations from industrial and mine waste waters. While KAD is also stable under alkaline conditions (up to pH 13) the solubility of most of the abovementioned cations is negligible and, thus, the selectivity of KAD could not be tested.

EXAMPLE 5 pH dependence of Pb ^* Exchange

0.25 g of K-KAD was dispersed both in 100 ml of 0.1 M

NaN0₃ solution and in 0.1 M Ca(N0₃)₂ solution, each containing 100 ppm Pb ^*. The pH of the solutions was adjusted using dilute HN0₃ or dilute NaOH solutions as appropriate. The solutions were stirred at room-temperature (20^βC) for 24 hours, the KAD then removed by centrifuge and the solutions analysed for remaining Pb^2*. This analysis then gives the amount of Pb^2* removed from solution at the particular pH. Details of these experiments are given in Table 5 below.

Table 5 Percentage of Pb ^* Removed from Solution at Various pH

EXAMPLE 6 Use of KAD as a water softener or detergent builder in providing sequestering of Ca^2* and Mg^2* in preference to Na^* in aqueous solutions.

Eighty milligrams of KAD powder is dispersed and stirred in 25ml of four different solutions for a period of two hours, after which KAD is removed from the supernatant. The supernatant is analysed for the concentrations of Mg 2+ and Ca ^*. The four different aqueous solutions contain: (i) lOppm Ca^2* and Mg^2* in distilled water at 18°C (the control sample), (ii) lOppm of Ca 2+ and Mg 2* in a 0.1M NaCl solution at 18 C, (iii) lOppm of Ca 2+ and Mg 2* in a 0.1M NaCl solution at 50°C and (iv) lOOppm of Ca^2* and Mg^2* in a 0.1M NaCl solution at 18°C. Data from these experiments are summarised in Table 6.

Table 6 Comparison of Ca ^* and Mg ^* Selectivity

As indicated in Table 6, KAD shows a capability to sequester Ca^2* and Mg ^* from solution which is suitable application as a detergent builder or water softener. In some applications for which KAD is to be used as a sequestering agent for the selective removal of cations from aqueous solution, it may be necessary to utilise KAD in a form which is not as a dispersed powder. KAD in its as-prepared form has a very fine particle or aggregrate size and disperses readily. In some applications, this property may hinder exploitation of the exchange properties because the physical separation of the exchanged KAD from the treated aqueous solution may be difficult or expensive.

For applications which require a mechanically stable monolithic body of various shapes, KAD can be combined with an organic polymer or with colloidal silica to allow KAD to bind to itself thereby increasing significantly the overall aggregate size and reducing the problem of physical separation of exchanged KAD from treated solution. The bound material can then be formed into robust pellets or other aggregates, or can be bound to a substrate such as wood fibre to form cation selective filter paper. Examples of the process for the formation of pellets using either an organic polymer or colloidal silica are given below:

EXAMPLE 7 Process for binding KAD using polycarbonate resin

0.012 g of polycarbonate resin is dissolved in 20 ml of toluene. 2.5 ml of this solution is added to 0.2 g of KAD, equivalent to an addition of 0.075 wt % polymer. The resultant slurry is thoroughly homogenised using a mortar and pestle then dried at 40^βC for 30 minutes. Pellets are formed from this material using a pellet press and applying uniaxial pressure of about 500kgcm-².

EXAMPLE 8 Process for binding KAD using colloidal silica

0.0304 g of Ludox AM (du Pont) is dissolved in 0.6 ml of water. 0.3 ml of this mixture is added to 0.25 g of KAD, equivalent to an addition of ~2 wt % colloidal silica. An additional 0.9 ml of water is then added and the slurry homogenised using a mortar and pestle then dried at 85"C for 18 minutes. Pellets are formed from this material using a pellet press and applying uniaxial pressure of about 500kgcm^" . The pellets are finally heated at 85^βC for 1.25 hours.

KAD which has been bound using either organic polymer or colloidal silica into monolithic pellets or discs retains its cation exchange properties to the abovementioned cations. This property of KAD is shown by the example given below.

EXAMPLE 9 Selectivity of KAD towards Cu^2* when bound into pellets

The following experiments were performed for KAD pellets prepared using both polycarbonate resin and colloidal silica as binding agents.

2 x 0.015 g KAD pellets are placed in 5 ml of 0.1 M NaN0₃ solution containing 100 ppm Cu ^*. The solutions were stirred at room-temperature (20^*C). After 24 hours one pellet was removed and 2.5 ml of the solution removed for analysis for remaining Cu ^*. The remaining solution was stirred at room-temperature for a further 2 days after which the second pellet was removed and the remaining solution again analysed. These data allow determination of the amount of Cu ^* removed from solution using these bound pellets of KAD and are given in Table 7. Table 7

Percentage of Cu 2* Removed from Solution using KAD Pellets with various binders

Time Colloidal Polycarbonate (days) Silica Resin

70 37

94 94

Example 10 Comparison of KAD selectivity for various cations.

A suite of exchange experiments were conducted using samples of KAD prepared as in Example 1 (from kaolinite) and in Example 2 (from halloysite). In each case, the exchange experiments with other cations were conducted in a 0.1 M NaN0₃ solution for 16 hours at room temperature. Typically, 90 mg of KAD was dispersed in 30 ml of solution. Results for these exchange experiments, in which the percentage removal of cation from solution was measured, are given in Table 8. Unless otherwise stated in this Table, the pH of the exchange solution was close to neutral. The concentrations of cations before and after exchange were determined using Atomic Absorption Spectroscopy, except in the case of Nd^3* and U0₂ ^2* for which UV/visible spectroscopy was used.

Table 8

Selectivity of KADs described in Examples 1 and 2 towards various cations

EXAMPLE 11 Synthesis of KAD at elevated pressure and higher temperature.

1.0 g of kaolinite obtained from Weipa, Queensland, Australia, and 4.0 g of potassium fluoride were thoroughly mixed with 3 ml of water. The mixture was transferred into a teflon sealed pressure vessel and placed in an oven at 150^βC. The vessel reached 80^βC within 5 minutes and 150^*C after a further 20 minutes. The vessel was held at this temperature for 5 minutes then removed from the oven and cooled to below 80°C. The reaction products were then dispersed in 100 ml of distilled water and centrifuged until the solid fraction has completely settled. The elute containing the excess salt and a small amount of the weakly soluble fluoride byproducts was decanted. This rinsing process was repeated until no further fluorine could be detected in the elute by addition of silver nitrate solution; typically after 3 to 4 rinses. The remaining solid was dried at 110^βC in air and comprises a mixture of KAD, starting kaolinite and relatively insoluble fluoride byproducts with a combined weight of 1.25 g. Figure 8 shows the XRD pattern of the solid reaction products.

EXAMPLE 12 Synthesis of KAD using NaF as the reagent. 0.25 g of kaolinite obtained from Weipa, Queensland, Australia, and 1.25 g of sodium fluoride were thoroughly mixed with 5 ml of water. The mixture was transferred into a teflon sealed pressure vessel and placed in an oven at 200^βC for 20 hours. The reaction products were then dispersed in 100 ml of warm (36 - 40^βC) distilled water and centrifuged until the solid fraction had completely settled. The elute containing the excess salt and a small amount of the weakly soluble fluoride byproducts was decanted. This rinsing process was repeated, 6 to 8 times, until no further fluorine could be detected in the elute. The remaining solid was dried at 110^*C in air and comprised a mixture of Na-KAD, starting kaolinite, and insoluble fluoride byproducts with combined weight of 0.39 g. Figure 9 shows the XRD pattern of the solid reaction products. EXAMPLE 13 Synthesis of KAD using either RbF or CsF as the reagent.

0.5 g of kaolinite obtained from Weipa, Queensland, Australia, and 5.0 g of rubidium fluoride or 7.0 g of cesium fluoride are thoroughly mixed with 1 ml of water. The mixture was heated in an oven at 110^*C for 3.5 hours. The reaction products were then dispersed in 40 ml of distilled water and centrifuged until the solid fraction had completely settled. The elute containing the excess salt and a small amount of the fluoride byproducts was decanted. This rinsing process was repeated, 3 to 4 times, until no futher fluoride could be detected in the elute. The remaning solid was dried at 110°C in air and comprised a mixture of M-KAD (M = Rb or Cs), starting kaolinite and relatively insoluble fluoride byproducts with combined weight of 0.86 g in the case of M = Rb and 0.85 g in the case of M = Cs. Figure 10 shows the XRD patterns of products for both reactions using either salt. For KAD prepared using RbF, a single broad peak is observed near the centre of the broad hump corresponding to a d-spacing of 3.16 _ (Figure 10a). In the case of KAD prepared using CsF, a similar diffraction pattern is observed, except that the broad hump is weaker and the peak has shifted slightly corresponding to a d-spacing of 3.25 _ (Figure 10b).

Kaolin Amorphous Derivatives which have been exchanged by transition metals or lanthanides with readily accessible lower valence states (e.g. Cu¹¹ - Cu¹ - Cu°, Ni" - Ni°, Co¹¹- Co⁰), have been reduced by heating under a stream of hydrogen gas at 400-500°C. While there is a small degree of unmixing of the metal observable by XRD the majority of the reduced metal remains associated with the KAD. The specific surface of the KADs decreases only slightly upon reduction under these conditions. This subsequent processing of KAD provides an ideal environment for metal-catalysed REDOX reactions with a wide variety of organic compounds. Specific examples of this application are given below.

EXAMPLE 14 Dehydrogenation of methanol to methyl formate using Cu-KAD as catalyst.

Cu-KAD is activated by reducing it overnight under H₂ at 400°C. Methanol vapour is passed over the catalyst at 200-220°C in a stream of N₂. The reaction products and unreacted methanol were trapped using a liquid N₂ trap and analysed immediately using H NMR spectroscopy. The mole percent of total phases obtained based on the NMR analysis was methanol:methylformate:dimethylether 74:19:7.

EXAMPLE 15 Dehydrogenation of ethanol to acetaldehyde using Cu-KAD as catalyst.

Cu-KAD is activated by reducing it overnight under H₂ at 400°C. Ethanol vapour is passed over the catalyst at 300°C in a stream of N₂. The reaction products and unreacted ethanol were trapped using a liquid N₂ trap and analysed immediately using H NMR spectroscopy. The mole percent of total phases obtained, based on the NMR analysis, was ethanol:acetaldehyde 56:44.

Whilst the above has been given by way of illustrative example of the invention, many modifications and variations may be made thereto by persons skilled in the art without departing from the broad scope and ambit of the invention as herein set forth. Figure Captions

Figure 1. ²⁷A1 magic angle spinning NMR spectra of KAD prepared from Weipa kaolinite according to Example 1, (a) after rinsing with water and (b) after rinsing with KOH. Spinning side bands are indicated by * .

Figure 2. ²⁹Si magic angle spinning NMR spectra of KAD prepared from Weipa kaolinite according to Example 1, (a) after rinsing with water and (b) after rinsing with KOH. Spinning side bands are indicated by * .

Figure 3. Transmission electron micrograph of (a) Weipa kaolinite grains before reaction and (b) KAD grains after reaction according to Example 1. Both images are at 250,000x magnification. Note the significant change in morphology and size of grains after the reaction to form KAD.

Figure 4. Transmission electron micrograph of (a) Matuara Bay tubular halloysite grains before reaction and (b) KAD grains after reaction according to Example 2. Both images are at 250,000x magnification. Note the significant change in morphology and size of grains after the reaction to form KAD.

Figure 5. Plot showing the rate of exchange of Pb^2* with KAD following the method given in Example 4 for three different solution temperatures. The plot shows the percentage of Pb^2* remaining in solution over time.

Figure 6. X-ray powder diffraction patterns of (a) Weipa kaolinite, (b) KAD which has been prepared from Weipa kaolinite according to Example 1, after rinsing with water and (c) KAD after rinsing with KOH. Diffraction peaks due to anatase, which is an impurity in the starting material, are indicated by +, and the poorly soluble flouride byproducts are indicated by * .

Figure 7. X-ray powder diffraction patterns of (a) Mataura Bay halloysite, (b) KAD which has been prepared from Mataura Bay halloysite according to Example 2, after rinsing with water and (c) KAD after rinsing with KOH. Diffraction peaks due to anatase, which is an impurity in the starting material, are indicated by +, and the poorly soluble flouride byproducts are indicated by * .

Figure 8. X-ray powder diffraction pattern (CuKa) of KAD which has been prepared from Weipa kaolinite at elevated pressure and 150°C using KF as the reagent according to Example 11, after rinsing with water but before rinsing with KOH. Diffraction peaks due to unreacted kaolinite are indicated by + and the poorly soluble flouride byproducts are indicated by * .

Figure 9. X-ray powder diffraction pattern (CuKa) of KAD which has been prepared from Weipa kaolinite using NaF as the reagent according to Example 12, after rinsing with water but before rinsing with KOH. Diffraction peaks due to unreacted kaolinite are indicated by + and the poorly soluble flouride byproducts are indicated by * .

Figure 10. X-ray powder diffraction patterns (CuKa) of KADs which have been prepared from Weipa kaolinite using (a) RbF and (b) CsF as the reagent according to Example 13, after rinsing with water but before rinsing with KOH. Diffraction peaks due to unreacted kaolinite are indicated by + and the poorly soluble flouride byproducts are indicated by * .

Claims (23)

CLAIMS :

1. An amorphous derivative of one of the kaolin group minerals.

2. An amorphous derivative of kaolinite and/or halloysite.

3. An amorphous derivative as claimed in Claim 1 which is characterised by a Al Magic-Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR) spectrum having a dominant peak in the range 70-40ppm relative to A1(H₂0)₆ ^3* .

4. An amorphous derivative as claimed in Claim 3 wherein the dominant peak is centred on about 55ppm.

5. An amorphous derivative as claimed in Claim 1 which is characterised by a BET surface area which is between 45 m g^" to 400m g^" .

6. An amorphous derivative as claimed in Claim 1 wherein the BET surface area is between 100 m²g^-1 and 250 m²g^"1.

7. An amorphous derivative as claimed in Claim 1 which is characterised by a cation exchange capacity of 50-450 milliequivalents per lOOg.

8. An amorphous derivative as claimed in Claim 7 wherein the cation exchange capacity is about 300 milliequivalents per lOOg.

9. An amorphous derivative as claimed in Claim 7 which exchanges the following cations with potassium: the alkalis - NH₄ ^*, Li^*, Na^*, Rb^* and Cs^*; the alkaline earths - Mg^2*, Ca ^*, Sr ^*, and Ba ^*; the transition metals - Cr^3*, Mn^2*, Co^2*, Ni^2*, Cu ^*, Zn ^*, Ag^*, Cd^2*, H^2* and the heavy metal Pb ^*; the lanthanides La ^* and Nd ^* and the actinide U0₂ ^2* .

10. An amorphous derivative as claimed in Claim 7 which is highly selective in its cation exchange towards the metals:

_ P,b 2* . C m.u 2*, C_d-2+, .N.i.2+, C_o2+, C_r3+ S„r2+, Z_n 2*, -N.d,3+ and, .U.0_₂2+.

11. An amorphous derivative as claimed in Claim 7, which upon exchange with the cations listed in Claim 9, retains a BET surface area value of between 45 and 400m g^"1.

12. An amorphous derivative as claimed in Claim 7 which is chemically stable over a range of pH conditions from pH~2.0 to pH~12.

13. An amorphous derivative as claimed in Claim 12 which shows a cation exchange capacity between 50 and 450meq/100g over a range of pH conditions from pH~2.0 to pH~12.

14. A process for the preparation of an amorphous derivative of one of the kaolin group minerals, which process comprises reacting a kaolin group mineral with a reagent which converts the majority of the octahedrally coordinated aluminium in the kaolin group mineral to tetrahedrally coordinated aluminium.

15. A process as claimed in Claim 14 wherein the reagent is selected from the group consisting of metal halides and ammonium halides.

16. A process as claimed in Claim 14 wherein the reagent is an alkali metal halide.

17. A process as claimed in Claim 16 wherein the alkali metal halide is potassium fluoride.

18. A process as claimed in Claim^' 14, which comprises reacting the kaolin group mineral with an aqueous alkali metal halide, wherein the mole ratio of the alkali metal halide (MX) to the kaolin group mineral (Al₂Si₂0₅(OH)₄) is from 5 to the saturation concentration of the alkali metal halide.

19. A process as claimed in Claim 18, in which the mole ratio of the alkali metal halide to the kaolin group mineral is in the range of 15 to 25.

20. A process as claimed in Claim 14, in which the kaolin group mineral is kaolinite and the reaction conditions comprise reaction with an alkali metal halide at a temperature up to 250°C for a time period of up to 100 hours.

21. A process as claimed in Claim 20, in which the reaction temperature is between 70°C and 150°C and the time period of reaction is between 1 minute and 100 hours.

22. An amorphous derivative of one of the kaolin group minerals in combination with an organic polymer or colloidal silica which allows the derivative to be formed into monolithic shapes and retain its essential properties.

23. An amorphous derivative of one of the kaolin group minerals substantially as herein described with reference to Example 1 or Example 2.