WO1995019398A1

WO1995019398A1 - Synthetic zeolite pigments

Info

Publication number: WO1995019398A1
Application number: PCT/EP1995/000101
Authority: WO
Inventors: Stuart William Carr; Florence Hollway
Original assignee: Crosfield Limited
Priority date: 1994-01-13
Filing date: 1995-01-11
Publication date: 1995-07-20
Also published as: AU1386595A; GB9400579D0

Abstract

A process for effecting cationic modification, especially to give a colour change, of particular synthetic zeolite pigments at relatively low temperature under mild conditions, comprises: (a) contacting the pigment with a cation-containing or cation-yielding composition at a temperature of up to 300 °C, preferably up to 150 °C, for a period of time sufficient to effect a desired degree of cationic modification of the zeolite structure; and (b) recovering therefrom the resulting cationically modified synthetic zeolite pigment. The cationic modification is preferably the incorporation or ion exchange of foreign cations, e.g. cations of one or more transition or main group elements, particularly one or more heavy metals, which effects a colour change in the pigment.

Description

SYNTHETIC ZEOLITE PIGMENTS

FIELD OF THE INVENTION

This invention relates to synthetic zeolite pigments and more particularly to a method for changing the colour thereof.

BACKGROUND OF THE INVENTION AND PRIOR ART

Zeolites constitute a family of microporous crystalline aluminosilicates. Currently there are known over thirty natural zeolite minerals and more than fifty synthetic zeolite minerals. The framework of these structures consists exclusively of tetrahedral oxides of aluminium and silicon, though other atoms which form tetrahedral coordination with oxygen have also been reported (Szostak, Molec. Sieves, 1989; Breck, Zeo. Mol. Sieves. 1974). As the charge on the framework is anionic, cations are located within the cavities and channels in the structure to balance the framework charge. A unique feature of the zeolites is that the cations which are located in the cavities and channels can be exchanged by other cations through an ion exchange process. The size of these channels and cavities is greater than 2.5 A which allows molecules such as water and oxygen to be adsorbed. This adsorption is generally reversible.

Every zeolite can be defined by its chemical composition and unique x-ray powder diffraction pattern which defines the framework topology or structure. Both composition and structure, as identified by the x-ray powder diffraction pattern, are necessary to fully define a zeolite material.

Though each framework topology is unique, structures can be classified by building units which compose the topology. Zeolites can sometimes be classified by these building units (see D. W. Breck, Zeo. Mol. Sieves, 1974; W. Meier and D. H. Olson, Atlas of Zeolite Structure Types. Revised Edition 1992). The beta cage, for example, is a known structural unit for a number of zeolite topologies, including type A, faujasite, EMC-2, ZK-5, and rho.

X-ray powder diffraction is a well known and accepted method of identifying unique crystal structures. Chemical composition can alter the position and intensities of the diffraction lines by small amounts, but it is in general considered to be a structure characterisation technique independent of composition and is frequently used as a fingerprint technique to identify aluminosilicate framework topologies (J. B. Higgins, Compilation of Simulated X-ray Powder Diffraction Patterns of Zeolites, 1989).

Many zeolites have both unique chemical compositions and diffraction patterns, but some may have similar compositions or diffraction patterns that differ in the other required parameter. For example, the zeolite identified as Linde Type A has a chemical composition of

Na₂0.A1₂0₃.2Si0₂.4.5H₂0 and a unique x-ray powder diffraction pattern, while the zeolite identified as zeolite alpha has a similar x-ray powder diffraction pattern but a chemical composition of (Na,TMA)₂0.A1₂0,.4.8Si0₂.7H-0. Zeolites beta and ZSM-5 have the same chemical composition but differ greatly in their x-ray powder diffraction patterns. Zeolites Y and ZSM-20 have similar chemical compositions and x-ray powder diffraction patterns which contain many of the same lines, though it is the respective x-ray diffraction pattern taken as a whole which characterise the two different materials. Thus, the fact that the ZSM-20 material has an x-ray powder diffraction pattern which contains extra lines compared with that of the Y-type material means that it is structurally a different material, and indeed is defined and patented as such; see for example US 3972983 (ZSM-20) and US 3130007 ( zeolite Y) .

Other properties which are representative of zeolites include their well-defined particle size. It is well known that zeolites have a particle size typically ranging between about 0.1 and 300 microns. What makes the zeolites unique from other aluminosilicates, however, is their adsorption and ion exchange properties. Adsorption of molecules such as water, oxygen, n-hexane and cyclohexane is dependent upon the structure of the material as well as its composition. For example, zeolite type A exhibits different adsorption properties depending upon the nature of the exchange cation: Ca²' exchanged type A zeolite adsorbs water, oxygen and n- hexane while

Na^* exchanged type A zeolite adsorbs water and oxygen only. K^* exchanged type A zeolite adsorbs water only.

The mineral lapis lazuli, a natural pigment known for centuries, is noted for its brilliant blue colour, permanence and alkaline stability. The synthetic analogue is better known as ultramarine blue. Uses for these materials include printing inks, textiles, rubber, artists' colours, plastics, cosmetics, paints and laundry blue. Ultramarine is considered to be non-toxic and has been approved by the US Food & Drug Administration (FDA) for food packaging. The structure of this mineral and synthetic analogue is based on the sodalite framework topology. The x-ray powder diffraction pattern data of the synthetic material as commonly commercially available (e.g. as described for example in Kirk Othmer, Encyclopaedia of Chemical Technology, 3rd Edition (1982), Volume 17, p. 827, Pubd. John Wiley & Sons) is shown in Table 1 of the accompanying tables. These materials are crystalline sulphur containing sodium aluminosilicates with a definite structure as defined by their x-ray powder diffraction pattern.

The ultramarines are typically prepared using clay, a sodium source, a carbon source and a sulphur source, which are mixed together and calcined, first under reducing conditions (yielding ultramarine green), then under oxidising conditions (yielding ultramarine blue). Commercially, very high temperatures, typically in excess of 750°C, and times of the order of several hours to weeks are required to complete the synthesis. Examples of disclosures of such processes include United States Patents Nos 2441950 and 2544695. Also to be mentioned are United States Patents Nos 2535057, 2544693 and 2759844, which disclose the production of ultramarine blue from a synthetic crystalline aluminosilicate with the sodalite structure. Representative treatment in these references include calcination under non-oxidising conditions at 600°C or higher, preferably from about 740 to 900°C (which yields ultramarine green), then under oxidising conditions, e.g. with sulphur dioxide, at about 500 to 800°C (which yields ultramarine blue). Disclosed temperatures and other conditions vary slightly from reference to reference.

SU-A-1638147 (1991) discloses the preparation of what is said to be ultramarine blue pigment, by subjecting a mixture of type P zeolite, soda, sulphur and carbon black (as reducing agent) to a multi-stage heat treatment, comprising heating for 50-60 minutes at 380-400°C, then for 120-150 minutes at 690-710°C, and then for 50-60 minutes at 450-480°C. In the highest temperature heating step of this process, however, the P-type structure of the zeolite is believed to break down.

A wide range of particle sizes, e.g. from about 0.5 to about 100 microns, are encountered in synthetic ultramarine blue as produced by the above known methods. Thus, crushing, grinding or other size separation of the product is required in order to obtain particles of pigment of preferred average size, e.g. not more than about 5 or 10 microns.

Although the known ultramarines contain charge balancing cations located within the structure, these materials normally do not exhibit appreciable adsorption or ion exchange properties, because of the high density of their structure and the smallness of the pores therein. JP-A-049968 (1978) discloses a process for making ultramarine blue from a synthetic zeolite of type A, X or Y, preferably type A, having a particle size of I to 5 microns. The starting materials, which include sodium pentasulphide and optionally a reductive material as well as the zeolite, are calcined in a nitrogen atmosphere at 600 to 900°C, preferably 750 to 850°C, for up to four hours, yielding ultramarine green. The ultramarine green is heated in a sulphur dioxide atmosphere at 500°C for one hour, yielding ultramarine blue. The x-ray powder diffraction pattern, which is shown in Table 1, corresponds largely to that of the commercial ultramarine blue based on the sodalite structure. It is well known in the literature that zeolites of type A structure can convert to the sodalite structure via a solid state transformation in the presence of sodium salts at high temperatures.

JP-B-047222 (1981) discloses the preparation of an ultramarine blue pigment which exhibits an x-ray powder diffraction pattern containing five strong lines corresponding to 7.14 A, 4.11 A, 3.72 A, 3.30 A and 3.00 A spacing, two medium strength lines at 4.36 A and 3.42 A spacing and one weak line corresponding to 5.05 A spacing. This diffraction pattern is shown in Table 1. The crystal system is identified as cubic with a lattice constant of what is stated to be 123 A. The blue pigment was prepared by mixing zeolite type A with an alkali metal sulphide A₂S_X, where A is the alkali metal and x is greater than 1, and heating the material at a temperature from 300 to 600°C in a non-oxidising atmosphere, then heating the resultant yellow/green product in an oxidising atmosphere at a similar temperature, yielding the final blue pigment.

US 2723917 (1955) discloses a process for making ultramarine pigments using a similar two-stage method as in the two Japanese prior art references mentioned above, but in which the second, oxidative step is carried out, still in the gas phase, using a mixture of air and water vapour as the oxidising agent. Temperatures of from about 100 C to about 550°C, preferably 250-300°C, are used for the second oxidative step of the process.

Known synthetic ultramarine pigments prepared by the prior art methods disclosed above generally exhibit limited ranges of colour, and indeed as prepared are normally either blue ( "ultramarine blue" ) or green ( "ultramarine green" ) . For use in many applications however, pigments of other colours are desirable.

It is known that these synthetic zeolite pigments can be prepared so as to have various colours principally by appropriately selecting the identity and relative amount of foreign cations present within the zeolite structure. The foreign cations may be the same or different from the cations provided by the starting zeolite itself, though generally at least one species of foreign cation must be introduced to give a particular desired characteristic colour. The additional cations may be provided either by means of being already incorporated in the zeolite starting material from which the pigment is prepared or alternatively may be provided in one or more of the other starting materials, eg. as the appropriate sulphide.

Also known is a method of changing the colour of an already prepared synthetic zeolite pigment, comprising heating the pigment at a moderately high temperature, e.g. up to about 200°C, in an atmosphere of for example chlorine, hydrogen chloride or ammonium chloride vapour or other suitable reagent for a period of time sufficient to effect a desired colour change.

Because of the low ion exchange propensity of many of the prior art ultramarine pigments once formed, it is often difficult to effect desired colour changes in post-preparative steps where the introduction or exchange of foreign cations is required. Whilst it may be possible to effect certain colour changes by means of high temperature treatments such as that mentioned immediately above, such additional steps mean an overall more costly and lengthy procedure, and furthermore may still pose limitations on those foreign cations and/or amounts thereof which may be incorporated into the zeolite structure and thus the range of and ease with which desired colour changes can be effected.

SUMMARY OF THE INVENTION

Surprisingly, we have now found that certain synthetic zeolite pigments are susceptible to relatively low temperature ion introduction and/or exchange under mild conditions, which enables the colour of such pigments to be changed or selected easily and cheaply, or some other form of cationic modification similarly effected, without the need for the bulky, expensive and such safety-oriented equipment and techniques of the prior art.

Accordingly, the present invention provides a process for effecting cationic modification of a synthetic zeolite pigment, comprising:

(a) contacting the pigment with a cation-containing or cation-yielding composition at a temperature of up to about 300°C, preferably up to about 150°C, for a period of time sufficient to effect a desired degree of cationic modification of the zeolite structure; and

(b) recovering therefrom a resulting cationically modified synthetic zeolite pigment.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

Preferred embodiments of the invention will now be described in detail. In the accompanying tables, which follow the Examples further below: Table 1 shows x-ray powder diffraction patterns of the following prior art materials: a type 4A zeolite as used as the starting material for preparing preferred synthetic zeolite pigments suitable for cationically modifying in accordance with the invention; conventional commercially available ultramarine blue pigment (as described in the Kirk-Othmer reference referred to above) ; the blue ultramarine pigment prepared as disclosed in JP-A-049968 (1978); the blue pigment prepared as disclosed in JP-B-047222 (1981);

Tables 2 and 3 each show the x-ray diffraction pattern of a particular cationically modified synthetic zeolite pigment in accordance with the invention, prepared by Examples 1 and 2, respectively, hereinbelow; and

Table 4 shows the X-ray diffraction pattern of the pigment prepared in Comparative Example 5 hereinbelow.

The identity of the cations which are introduced into the zeolite structure to preferably effect the colour change of the pigment is preferably selected according to the particular colour which it is desired to obtain or to some other form of cationic modification which it is desired to effect. Most cations, especially those of transition and main group elements, e.g. heavy metals, which are preferred cations in accordance with the invention, give characteristic colours when incorporated into the zeolite structure, so by selecting an appropriate species of cation, a particular desired colour can be obtained. The cations may comprise one species only or a mixture of two or more species. The latter may for example be useful in effecting colour changes not normally obtainable with a single cation species only.

Examples of particular cations suitable for use in the invention include those of a variety of transition and main group elements, especially heavy metals, for example zinc, manganese, titanium, vanadium, chromium, platinum, nickel, cobalt, iron, copper and the lanthanides. Zinc cations, for example, give cationically modified pigments having characteristic intense pink colours, while other metal cations may give other intense colours.

The composition with which the pigment is contacted in the process of the invention may be either cation-containing, which means that the composition comprises cations per se, e.g. in solution, or cation-yielding, which means that the composition comprises one or more species which generate or otherwise release cations under the conditions of the reaction.

As suitable "cation-containing" compositions, solutions of the appropriate cations are well known and widely available in the art. As suitable "cation-yielding" compositions, metal vapours or plasmas and compositions which comprise compounds such as organic alkyl-metal complexes, e.g. dialkyl-metal complexes, metal carbonyl complexes, metal hydrides or the like, may be used. Generally, however, it is important that a cation-yielding material releases the appropriate cations for incorporation into the pigment structure under the relatively mild conditions under which the reaction is carried out in accordance with the invention.

The composition providing the cations with which the zeolite pigment is contacted in the process of the invention is preferably a solution of the cations per se in one or more solvents or carriers. Water is particularly preferred, though other solvents/carriers such as organic liquids, oils etc. may also be suitable. In particularly preferred embodiments, the composition is an aqueous solution or slurry of one or more salts of the appropriate cation or cations. Whilst cation- containing salt solutions are preferred, slurries or pastes, ie. hydrated salt systems, may also be suitable. Preferably the medium in which the treatment of the pigment is carried out has a pH of at least about 6 or 7.

Preferably, the above preferred process of the invention is carried out by suspending or otherwise dispersing the pigment to be cationically modified in the cation- containing composition, and heating (or cooling) the mixture to the required temperature and maintaining it so for the required period of time, eg. by refluxing.

In accordance with the invention, the zeolite pigment is contacted with the cation-containing or cation-yielding composition at a temperature of up to about 300°C, preferably up to about 150^βC. The temperature is preferably in the range -20 to +120°C, i.e. particularly when the composition is an aqueous solution, the process may be carried out as anything from a cooled (eg. ice-cooled) system up to a boiling or refluxed system.

The temperature of the reaction may generally be selected so that, in combination with the reaction time and other parameters, eg. the identity of the zeolite pigment and the cations to be incorporated into the structure thereof, the appropriate degree of cationic modification is effected, especially to give (in the preferred process) the desired colour change of the pigment. Appropriate reaction temperatures and times may therefore vary but will be readily determinable for any given system by persons skilled in the art on the basis of experiment and/or trial and error.

The synthetic zeolite pigment which is subjected to the process of the present invention may be any zeolite pigment which has a sufficiently open structure which allows the introduction and/or exchange, under the mild conditions of the process, of the cations with which it is to be modified.

In one preferred embodiment of the invention the synthetic zeolite pigment which is cationically modified is a novel synthetic zeolite pigment prepared according to the processes disclosed in our copending United Kingdom patent application No. 9400574, dated 13th January 1994, the content of which is incorporated herein by reference. In this first preferred preparative process the synthetic zeolite pigment is prepared by the following steps: -

( i ) heating a mixture comprising crystalline aluminosilicate zeolite and each of a reducible sulphur source, a reducing agent and a source of cations under non-oxidising conditions at a temperature at which the zeolite substantially retains its framework structure, preferably a temperature of from about 300 to about 600°C; and

( ii ) recovering therefrom the said synthetic zeolite pigment.

Preferably the reducing agent is a source of carbon, eg. a carbon-containing salt or elemental carbon, and the preferred starting zeolite material may be selected from type A, type X and type Y zeolites (or even a mixture of two or more of such materials ) .

In principal embodiments of the above process the recovery step may either be done immediately after the heating step (i) under non-oxidising conditions or, more preferably, is done following a second heating step carried out subsequent to the first, which second step comprises heating the product of step (i ) in an oxidising atmosphere at a temperature again at which the zeolite substantially retains its framework structure, e.g. a temperature of from about 300 to about 600°C, preferably from about 350 to about 550°C.

The inorganic pigment recovered immediately after the first, non-oxidising, heating step may for example have a colour corresponding to that of ultramarine green, though the colour may vary depending upon the reaction conditions, the structure of the starting zeolite and the chemical composition of the zeolite and other starting materials eg. it may be yellow, brown, red, etc., whereas the pigment recovered after the second, oxidising heating step will generally be of a colour corresponding to that of ultramarine blue.

According to a further aspect of the present invention, therefore, the colour of these prepared synthetic pigments may be changed by incorporation and/or exchange of one or more species of foreign cation at relatively low temperatures under mild conditions.

In another preferred embodiment of the invention the synthetic zeolite pigment which is cationically modified is a novel synthetic zeolite pigment prepared according to the processes disclosed in our copending United Kingdom patent application No. 9400580.8, dated 13th January 1994, the content of which is incorporated herein by reference. In this second preferred preparative process the synthetic zeolite pigment is prepared by the following steps: -

( i ) heating a mixture comprising crystalline aluminosilicate zeolite and sources of each of sulphur, cations and optionally a reducing agent under non-oxidising conditions at a temperature at which the zeolite substantially retains its framework structure, preferably a temperature of from about 300 to about 600°C;

(ii ) contacting the product of step (i) with an oxidising agent in the presence of a solvent or carrier at a temperature of up to 300°C; and

( iii ) recovering therefrom the said synthetic zeolite pigment. If a reducing agent is present, which may depend on the identity of the sulphur source, then a preferred reducing agent is a source of carbon, eg. a carbon-containing salt or elemental carbon. Preferred zeolite starting materials are type A, type X or type Y zeolites.

The inorganic pigment resulting from the first, non- oxidising, heating step may for example have a colour corresponding to that of ultramarine green though the colour may again vary depending upon the reaction conditions, the structure of the starting zeolite and the chemical composition of the zeolite and the other starting materials, eg. it may be yellow, brown, red, etc., whereas the pigment recovered after the second, oxidising step may generally be of a colour corresponding to that of ultramarine blue.

According to a yet further aspect of the present invention, therefore, the colour of these prepared synthetic pigments too may be changed by incorporation and/or exchange of one or more species of foreign cation at relatively low temperatures under mild conditions.

In other embodiments of the invention the synthetic zeolite pigment is a pigment prepared by any of the processes known from the prior art, particularly as disclosed in the prior art references mentioned above, and which has a sufficiently open structure to allow cationic modification thereof under the mild conditions of the process of this invention. In particular, synthetic zeolite pigments having similar structures, as represented by their x-ray diffraction patterns, to the two preferred pigments of our copending UK patent applications referred to above may also be suitable for cationic modification in accordance with the process of the present invention. For example, the pigment disclosed in JP- B-047222 (1981) may also be suitable.

Preferred embodiments of the present invention are further illustrated by the following Examples 1 to 5, which are not intended to limit in any way the scope of the claimed invention. The tables referred to in Examples 1 to 5 follow after the Examples.

Where given, x-ray diffraction data were collected using a Siemens D5000 automated diffraction system employing Θ-2Θ geometry and graphite monochromatised Cu K-alpha radiation. Diffraction data were recorded by step-scanning at 0.05 degrees of 2Θ, where 2Θ is the Bragg angle, and a counting time of 3 seconds for each step (sample identification) and 6 seconds for each step (crystallinity measurement) . The interplanar spacings d were calculated in Angstrom units (A) and the relative intensities of the lines I/I₀, where I₀ is the intensity of the strongest line, above background were derived with the use of a profile fitting routine. For unit cell measurement crystalline silicon powder was added to the sample as an internal calibrant. The relative intensities are given in terms of the following symbols: vs = very strong s = strong ms = medium strong m = medium mw = medium weak w = weak vw = very weak vvw = very very weak.

Examples

Example 1

This example illustrates the preparation of pink zeolite pigment by ion exchange of zinc salts on blue pigment in aqueous solution at ambient temperature.

Blue synthetic zeolite pigment was prepared according to the following method:-

A mixture of ground sulphur ( 9.2g) and ground anhydrous sodium acetate (3.3g) was added to hydrated 4A zeolite ( 5.7g ) . The complete raw material mixture was mixed with a mortar and pestle. The ground mixture was packed into a glass boat which was placed inside a tube furnace. This was purged of air under a flow of argon gas (0.25 1/hour) at ambient temperature, then heated in flowing argon until a temperature of 450°C was reached (approximately h hour) . The furnace was maintained at this temperature for L ^~ to 2 hours under flowing argon then switched off and allowed to cool to ambient temperature under the argon flow.

The resultant material had a bright yellow-green colour at this stage.

Yellow-green product prepared as above was packed into a glass boat which was placed inside the tube furnace. This was purged of air under a flow of argon gas (0.25 (/hour) at ambient temperature, then heated in flowing argon until a temperature of 450°C was reached (approximately 1/2 hour). At this point the gas was switched from argon to sulphur dioxide which was allowed to pass through the furnace at 0.25 (/hour with the temperature maintained at 450°C. After 2 hours, flow of sulphur dioxide was discontinued and flow of argon at 0.25 £/hour resumed. The furnace was switched off and allowed to cool to ambient temperature under argon. Pigment having an intense blue colour was obtained.

The resulting pigment was twice contacted with 0.5M aqueous zinc nitrate solution (100 mis) at room temperature for 2 hours. It was oven dried at 90-100°C. Pigment having an intense pink colour was obtained and was shown by x-ray powder diffraction to be crystalline with an x-ray powder diffraction pattern as shown in Table 2.

Examples 2 to 4 which follow illustrate that different colours can be obtained by variation of the concentration of exchanging cation and the contact time.

Example 2

A sample of the synthetic zeolite pigment (lOg), prepared according to the method described in Example 1, was contacted with 0.5M zinc nitrate solution (100 mis) at ambient temperature for four days with stirring to maintain the solid suspended. This procedure was performed twice. At the end of these procedures the product was isolated by centrifugation to give a sage green product. The material was dried at 95°C in air for one day to give a sage green material. The x-ray powder diffraction pattern was as shown in Table 3.

The pigment was analysed for sulphur, silicon, aluminium, sodium and zinc as follows:

For sulphur, the sample was subjected to fusion with sodium peroxide which converted all sulphur compounds to sulphates and simultaneously solubilised silica and aluminium. After acidification, dehydration of silica and filtration, the sulphate was precipitated as barium sulphate and finished gravimetrically.

For silicon and aluminium, the sample, was fused in sodium carbonate and the silica dehydrated, filtered and finished gravimetrically with HF purification. the residue was fused, added back to the main solution and this solution analysed for aluminium by ICP spectroscop .

For sodium, the sample was dissolved in a mixture of aqua regia and HF, fumed in perchloric acid and the sodium determined by flame emission spectroscopy.

Zinc was determined by atomic absorption spectroscopy.

The elemental composition was as given below: Element % (wt/wt)

Al 13.2

Si 12.2

Na 9.43

Zn 6.78

S 12.5

Example 3

Example 2 was repeated but using 0.05M zinc nitrate solution with two contacts each of two days at ambient temperature. The resultant material in this example was steel blue, with an essentially unchanged x- ray powder diffraction pattern.

The pigment was analysed for sulphur, silicon, aluminium, sodium and zinc in the same manner as in Example 2. The elemental composition was as given below:

Element % ( t/wt)

Al 11.6

Si 10.5

Na 13.1

Zn 17.2

S 18.7

Example 4

Example 2 was repeated but using 0.05M zinc nitrate solution with one contact of twenty four hours at ambient temperature. The resultant material was flesh coloured, with an essentially unchanged x-ray powder diffraction.

The pigment was analysed for sulphur, silicon, aluminium, sodium and zinc in the same manner as in

Example 2. The elemental composition was as given below: Element % (wt/wt)

Al 13.2

Si 12.3

Na 5.22

Zn 3.17

S 13.8

Example 5 (Comparative Example)

Example 2 was repeated but using conventional ultramarine blue pigment of the prior art. After this procedure the material was recovered, but no colour change had occurred and the X-ray powder diffraction pattern, as shown in Table 4, was essentially unaltered from that of commercial ultramarine blue, ie. based on the sodalite structure.

Element % (wt/wt)

Al 14.8

Si 17.6

Na 10.7

Zn 3.27

S 10.8

Table 1

Zeolite 4A Commercial Blue pigment of Blue pigment of

(as described in ultramarine JP-A-049968 (1978) JP-B-047222 (1981)

US 2882243) blue

d(A) d(A) d(A) d(A)

12.29 s 7.14 vvw 6. .43 m 7.14 s

8.71 ms 6.44 m 4. .54 vw 5.05 w

7.11 m 4.55 vw 3. .71 vs 4.36

5.51 m 4.03 vvw 2. .87 mw 4.11 s

5.03 vw 3.93 vvw 2. .62 m 3.72 s

4.36 vw 3.89 vvw 2. .43 vvw 3.42

4.11 m 3.79 vvw 3.30 s

3.71 s 3.71 vs 3.00 s

3.42 w 3.60 vw

3.29 m 3.41 vvw

2.99 m 3.35 vvw

2.90 w 3.30 vvw

2.754 w 3.19 vvw

2.688 vw 2.97 vvw

2.626 m 2.93 vvw

2.515 vw 2.88 m

2.464 vw 2.68 vw

2.371 vw 2.63 m

vs: very strong, s: strong, ms: medium strong, m: medium. mw: medium weak w: weak, vw: very weak, vvs: very very weak

Table 2 ( Pigment of Example 1 )

29 d relative intensity

10.06 8.79 w

12.30 7.19 m

13.94* 6.35 vw

15.97 5.54 w

17.50 5.06 w

18.62* 4.76 vw

20.28 4.38 mw

21.50 4.13 s

22.63 3.93 mw

23.81 3.73 vs

25.53* 3.49 mw

25.92 3.43 mw

26.90 3.31 s

29.70 3.01 s

30.63 2.92 w

31.82* 2.81 m

33.25 2.69 w

33.93 2.64 s

35.56 2.52 vw

36.29 2.47 mw

* these lines are due to the presence of impurities vs: very strong, s: strong, m: medium, mw: medium weak w: weak, vw: very weak

Table 3 ( Pigment of Example 2

2Θ relative intensity

7.22 12.24 w

10.39 8.51 w

12.46 7.10 m

16.12 5.50 w

17.63 5.03 w

20.40 4.35 mw

21.64 4.10 s

23.93 3.72 s

26.04 3.42 mw

27.08 3.29 s

29.91 2.99 s

30.79 2.90 mw

32.50 2.75 w

33.30 2.69 w

34.13 2.62 m

35.72 2.51 w

36.46 2.46 m

vs: very strong, s: strong, m: medium, mw: medium weak w: weak, vw: very weak

Table 4 (Ultramarine pigment of Comparative Example 5)

29 d relative intensity

12.42 7.12 ww

13.79 6.41 m

19.55 4.54 w

22.79 3.90 vw

24.01 3.70 vs

24.77 3.59 vw

26.12 3.41 vw

26.71 3.33 vw

27.10 3.29 vw

30.25 2.95 vvw

31.12 2.87 m

33.41 2.68 ww

34.18 2.62 ms

37.06 2.42 vw

39.69 2.27 mw

vs: very strong, s: strong, ms: medium strong, m: medium, mw: medium weak, w: weak, vw: very weak ww: very very weak

Claims

1. A process for effecting cationic modification of a synthetic zeolite pigment, comprising:

(a) contacting the pigment with a cation-containing or cation-yielding composition at a temperature of up to 300°C for a period of time sufficient to effect a desired degree of cationic modification of the zeolite structure; and

2. A process according to claim 1, wherein the cationic modification effects a change in the colour of the pigment.

3. A process according to claim 1 or claim 2, wherein the cations introduced into the zeolite structure are cations of one or more transition or main group elements.

4. A process according to claim 3, wherein the cations are cations of one or more heavy metals.

5. A process according to any preceding claim, wherein the composition comprises said cations per se in solution.

6. A process according to any one of claims 1 to 4, wherein the composition comprises one or more species which generate or otherwise release the said cations under the conditions of the reaction.

7. A process according to claim 5, wherein the composition is a solution of the said cations in one or more solvents or carriers.

8. A process according to claim 7, wherein the composition is a solution of a salt of the said cations.

9. A process according to claim 7 or claim 8, wherein the one or more solvents or carriers comprise water.

10. A process according to any preceding claim, wherein the pigment is contacted with the composition at a temperature of up to 150°C.

11. A process according to any preceding claim, wherein the pigment is contacted with the composition at a temperature of between -20 and +120°C.

12. A process according to any preceding claim, wherein the synthetic zeolite pigment is prepared by a process which comprises the following steps:

( i ) heating a mixture comprising crystalline aluminosilicate zeolite and each of a reducible sulphur source, a reducing agent and a source of cations under non-oxidising conditions at a temperature at which the zeolite substantially retains its framework structure; and

( ii ) recovering therefrom the said synthetic zeolite pigment.

13. A process according to any one of claims 1 to 11, wherein the synthetic zeolite pigment is prepared by a process which comprises the following steps:

(i ) heating a mixture comprising crystalline aluminosilicate zeolite and sources of each of sulphur, cations and optionally a reducing agent under non- oxidising conditions at a temperature at which the zeolite substantially retains its framework structure;

( ii ) contacting the product of step ( i ) with an oxidising agent in the presence of a solvent or carrier at a temperature of up to 300°C; and

( iii ) recovering therefrom the said synthetic zeolite pigment.

14. A process according to claim 12 or claim 13, wherein in step (i) the heating temperature is from 300 to 600°C.

15. A cationically modified synthetic zeolite pigment as prepared by the process of any preceding claim.

16. A cationically modified synthetic zeolite pigment according to claim 15, which has an x-ray powder diffraction pattern substantially as shown in any one of Tables 2 and 3 herein.

17. A method of changing the colour of a synthetic zeolite pigment, comprising: -

(a) contacting the pigment with a solution of metal cations at a temperature of up to 150°C for a period of time sufficient to effect the desired colour change of the pigment;

(b) recovering therefrom the resulting colour- changed synthetic zeolite pigment.

18. A method according to claim 17, wherein the metal cations comprise cations of at least one transition or main group element.

19. A method according to claim 18, wherein the metal cations comprise cations of at least one heavy metal.