Pillared trioctahedral micas and/or vermiculites are prepared. The process includes a conditioning operation for the partial reduction of the layer charge through an accelerated weathering process, and also includes a pillaring operation.

FIELD OF THE INVENTION
 The present invention is related to pillared trioctahedral-type natural
 micas and vermiculites, to a preparation method thereof, and to their
 applications.
 BACKGROUND OF THE INVENTION
 TECHNICAL BACKGROUND OF THE INVENTION
 Pillared interlayered smectites (PILCs) with a large variety of pillars
 have been described in the scientific literature (journals, patents),
 among which the Al-pillared clays are the most documented ones. Similar
 materials with pillars based on other elements such as Zr, Cr, Ti, Si, Fe,
 Ga, Si, Ta, V, Mo, Nb, combinations of two or more of these elements or
 combinations of one or several of those elements with others elements not
 mentioned above (as e.g. Ni, Cu, Co, etc.), rare-earth (La, Ce . . .
 )--containing pillars have been successfully prepared and reported in the
 literature. Pillared clays containing two or more elements in the pillars
 are also named mixed pillared clays.
 Pillared clays show interesting potentialities in catalysis, as catalysts
 or supports to catalytic phase(s) or in admixture with other catalysts or
 catalyst components (e.g. zeolites, metal oxides, etc.), especially as
 catalysts for e.g. hydrocarbons transformation. Pillared materials also
 find potential interest as adsorbents and in other domains such as in gas
 separation processes; as scavengers for heavy metals (treatment of waste
 water); in SO.sub.2 and NO.sub.x abatement; in purification of edible oil,
 cation selective composite membranes; as solid electrolytes; as host
 materials for (conducting) polymers; etc.
 Trioctahedral micas
 Trioctahedral micas refer to layered 2:1 sheet (or lamellar) silicates in
 which the octahedral layer is sandwiched between two adjacent tetrahedral
 layers and mainly contains divalent cations with the results that all the
 possible octahedral positions are occupied. They differ from dioctahedral
 micas (muscovite-type), where 2/3 of the octahedral positions are filled
 with mostly trivalent cations. The general formula of the end-member
 phlogopite mineral is K.sub.2 Mg.sub.6 (Si.sub.6 Al.sub.2)O.sub.20
 (OH,F)4. The structural substitutions mainly occur in the octahedral
 layers but also in the tetrahedral ones and are responsible for the wide
 range of chemical compositions of the trioctahedral micas. The high number
 of substitutions is at the origin of the high net negative layer charge in
 micas. Potassium is usually the dominant interlayer cation ensuring
 electroneutrality of the layers. Trioctahedral micas may contain
 substantial amounts of fluorine (replacing structural hydroxyls) which
 conveys resistance to weathering, hardness and thermal resistance. The
 principal cations in the octahedral layer of natural trioctahedral micas
 are Mg.sup.2+, Fe.sub.2+, Al.sup.3+ and Fe.sup.3+, with smaller
 proportions of Mn.sup.2+, Ti.sup.4+ and Li.sup.+. Phlogopites refer to
 trioctahedral micas in which more than 70% of the occupied octahedral
 sites contain Mg.sup.2+, whereas biotites define the micas where 20 to 60%
 of these sites are Mg.sup.2+ [Newman & Brown, in Chemistry of Clays and
 Clay Minerals, A. C. D Newman (Ed.), Mineralogical Soc. 6, Longman, 1987,
 p. 75]. The potassium ions located between the unit layers just fit into
 hexagonal cavities (perforations) in the oxygen plane of the tetrahedral
 layers. Adjacent layers are stacked in such a way that the potassium ion
 is equidistant from 12 oxygens, 6 of each tetahedral layer [R. E. Grim,
 Clay Mineralogy, McGraw-Hill, 1953, p.65]. In their original state,
 natural micas do not swell in the presence of water or polar solvents
 because the hydration energy of the interlayer potassium ions is
 insufficient to overcome the co-operative structural forces at the
 coherent edges of a cleavage surface [Newman & Brown, Nature 223, 175,
 1969].
 The absence of swelling properties of natural micas makes it impossible,
 without modifying the mineral, to obtain pillared intercalated forms
 equivalent to those readily obtained with swelling clays (smectites) in
 which the clay sheets are separated from each other by pillars of
 inorganic nature, which confer to these materials thermally resistant
 structural and textural characteristics such as permanent elevated
 spacings, high specific surface area and micropore volume, and surface
 properties (acido-basic, redox).
 Vermiculites
 Vermiculites belong to a group of hydrated aluminium silicates. These
 minerals may be considered as "swelling trioctahedral micas" containing
 Al-for-Si substitutions in the tetrahedral layers (as in micas), and Al-,
 Fe-, and Ti-for-Mg substitutions in the octahedral layers. Because of both
 types of substitutions, the overall negative charge of the structure
 results, as in micas, from an imbalance between the negative charge of the
 tetrahedral layer and the excess positive charge of the octahedral layer.
 As in micas and smectites, the excess negative charge is counterbalanced
 by cations located in the region between adjacent sheets which ensure
 electroneutrality of the layers. Most often, the interlayer cations are
 magnesium ions. The layer charge densities in vermiculites are
 intermediate between those of micas and smectites. Unlike micas,
 vermiculites may swell and the layers may expand when polar molecules are
 introduced in the interlamellar region but this swelling capability is
 much reduced compared with smectites. The interlayer charge balancing
 cations (magnesium ions) are exchangeable.
 Vermiculites (and a fortiori micas) could not be intercalated with bulky
 poly-hydroxy-aluminum species to form a pillared material exhibiting
 spacings of about 17-18 .ANG. (gallery height of about 8 .ANG.) as in
 pillared smectites, a failure which has been attributed to the high layer
 charge density of these minerals. Contacting vermiculite suspensions with
 Al.sub.13 -containing pillaring solutions led to expanded materials
 exhibiting only about 14 .ANG. spacings [references 1-7]. Taking advantage
 of the high spacings (27-28 .ANG.) developed upon adsorption of long chain
 amines and alcohols to introduce Al pillars was unsuccessful [reference
 5]. Preliminary dealumination of vermiculite by treatment with an aqueous
 solution of (NH.sub.4).sub.2 SiF.sub.6 followed by the addition of the
 pillaring solution did not result in materials with improved spacings
 [reference 7]. A mixture of a pillared fraction of vermiculite (with 18
 .ANG. spacing stable at 500.degree. C.) and of unpillared fraction was
 obtained upon contacting with Al.sub.13 -containing solutions a suspension
 of vermiculite that was previously treated with L-ornithine [reference 8].
 However, repeated attempts to reproduce the method were unsuccessful.
 State of the Art
 The documents U.S. Pat Nos. 5,200,378 and 5,017,537 are concerned with the
 pillaring of synthetic layered phosphates. Layered phosphates have nothing
 in common with natural micas. The intercalation is performed after a
 previous intercalation of an amine (amide or dimethyl sulfoxide) in order
 to expand the interlayers. Attempts to pre-swell vermiculite with a long
 chain amine or alcohol and to treat the expanded vermiculite with a
 pillaring solution did not allow to obtain 18 .ANG. Al-pillared
 vermiculite.
 The documents U.S. Pat. No. 5,340,657 and EP-0240359 deal with the
 Al-pillaring of synthetic sodium tetrasilicic fluor micas which have
 nothing in common with natural micas. The Na-TSF micas have only
 octahedral substitutions (Li for Mg or Mg for Al), but no aluminium in the
 tetrahedral layers. Natural micas have substitutions in both the
 tetrahedral (Al for Si) and octahedral (Al, Fe for Mg) layers. Na-TSF
 micas are synthesized in a soda-containing medium (thus no interlayer
 potassium as in natural micas). The presence of exchangeable Na in the
 interlayers as charge neutralizing cations confers swelling properties.
 Natural micas have potassium ions between the layers and do not swell in
 polar media. Na-TSF micas can be pillared when they are contacted with the
 pillaring solution. Nothing like occurs when doing so with natural micas.
 This is the principal reason for the prerequisited conditioning operation
 of the natural micas (aiming at the charge reduction of vermiculites and
 micas and conversion to homoionic form of hydrated ions). Synthetic
 Na-micas have, as hydrothermally synthetic layer materials, very small
 particle sizes. Particles of the order of 0.1 micron are preferred in the
 document EP-0240359 (p. 3, lines 8-10).
 The document U.S. Pat. No. 4,510,257 describes a method which allows to
 intercalate three-dimensional silicon oxide pillars from organo-silicon
 derivatives in the clay interlayers. The material is then calcined to
 decompose the organic moiety. Vermiculite is mentioned (yet no example of
 successful Si-pillared material is provided).
 The document WO98/00091 deals with the pillaring of synthetic layered
 silicate materials which have no octahedral layers and are thus different
 from either synthetic sodium fluor tetrasilicic "micas" or natural micas
 (as in our patent application), both of which having octahedral layers.
 SUMMARY OF THE INVENTION
 This invention describes a method for the obtention of pillared
 trioctahedral-type micas (PILMs) and vermiculites (PILVs) characterised by
 thermally stable interlayer distances, high specific surface areas and
 micropore volumes, and acidic properties. These features are similar to
 those found for equivalent pillared interlayered materials obtained from
 naturally occurring swelling clays, or smectites, (or their hydrothermally
 synthesised analogues) such as montmorillonites (bentonites), beidellites,
 hectorites (fluorhectorite and laponite, synthetic analogues), saponites,
 nontronites, rectorites (interstratified montmorillonite-muscovite),
 Ni-SMM and SMM (the so-called synthetic expandable mica-montruorillonite)
 to quote some of the main ones used in the preparation of pillared
 interlayered clays (PILCs).
 Pillaring is achieved after submitting the starting micas and vermiculites
 to a conditioning procedure consisting of chemical and thermal treatments
 which aim to reduce the layer charge density and replace the charge
 balancing potassium ions located in the interlayers of the initial micas,
 or the magnesium ions in the case of vermiculites, by hydrated cations
 such as f.i. sodium ions. The charge-reduced cation-exchanged (Na.sup.+,
 Ca.sup.+2, . . . ) forms of micas and vermiculites may be converted to any
 other cationic form(s) by simple exchange of the interlayer cations (f.i.
 Na.sup.+) by the desired element(s). Pillared micas and vermiculites are
 obtained by contacting Na-micas and Na-vermiculites with solutions
 containing the pillaring species, namely, polyoxohydroxymetal cations
 which intercalate between the layers according to a cation-exchange
 process, in a similar manner as for the obtention of pillared smectites.
 Successful insertion of Al-polymerised species is not restricted to the
 sole Al element. Substitution of Al in the pillaring solution by any one
 of the elements indicated below or mixtures thereof which have been
 successfully employed in the preparation of pillared smectites, give rise
 to equivalent pillared micas and vermiculites, thus offering materials
 with a wide variety of intercalated pillars and mixed pillars differing in
 the nature of the pillaring species and composition.
 It is one object of the present invention that the same preparation
 procedure may be equally applied to trioctahedral micas and vermiculites
 and wastes thereof (as defined below) to obtain pillared materials
 exhibiting the characteristic features of analogous materials prepared
 from smectites.
 In accordance with the aforementioned objectives, it is a particular object
 of the invention to find a new route to the pillaring of trioctahedral
 micas and vermiculites with solutions containing Al hydroxy-polymeric
 species often referred to as AlO.sub.4 Al.sub.12 (OH).sub.24 (H.sub.2
 O).sub.12.sup.7+ (in short, Al.sub.13) with Keggin-like structure
 [reference 9]. This objective is realized through the partial reduction of
 the layer charge density, which may be compared to an "accelerated
 weathering" process, and through the application of pillaring solutions in
 the form of partially hydrolysed Al solutions, the Al species in presence
 in these solutions having been identified [references 9-12].
 It is a further object that this invention is not restricted to the sole
 case of aluminium as the metal element of the pillar since, as stated
 above, substitution of Al in the pillaring solution by anyone of the
 elements Zr, Ti, Si, Cr, Fe, Ta, Nb, Ga etc. or combinations of different
 elements including lanthanides or mixtures thereof give rise to equivalent
 pillared micas and vermiculites.
 Therefore, it is an object of the invention to give access via the
 successful Al-pillaring of micas and vermiculites to the preparation of
 materials with different types of pillar species (based, e.g., on Zr, Ti,
 Si, Cr, Fe, Ta, Nb, Ga, etc, or combinations of different elements,
 including lanthanides) with possible uses in various catalytic reactions
 and other application areas.
 Further, the greater intrinsic structural stability of micas and
 vermiculites compared with smectites is of considerable interest in
 achieving pillared materials which possess improved resistance to thermal
 treatments, a weakness shared by all smectite-based pillared materials.
 Another interest of the method is the possibility to use micas and
 vermiculites with various particle sizes.
 Other objects of the invention include post-exchange and/or impregnation of
 the pillared materials, improvement of the acidic properties, use in
 fluidised bed applications.
 Further details will appear in the claims and in the description hereafter
 of preferred embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION
 General Description of the Pillaring Procedure
 Al-pillared micas and vermiculites exhibiting stable spacings (18 .ANG. and
 more for room temperature dried samples) are obtained after:
 i) a conditioning step which brings about a reduction of the layer charge
 density of the minerals and allows to convert the minerals in fully
 exchanged monoionic forms and
 ii) a pillaring step consisting of contacting the cation-exchanged minerals
 (monoionic forms) with the pillaring solution following any method known
 from the literature.
 Efficient pillaring is achieved provided that the conditioning treatment is
 properly carried out. Adequate conditioning can be controlled by
 characterising the solids at the different intermediate steps by use of
 suitable techniques and methods (e.g. X-ray diffraction, nitrogen sorption
 isotherms etc.). These controls may require washing and drying operations
 which are superfluous in the continuous preparation procedure.
 In the "standard method", the conditioning step of micas and vermiculites
 consists of four consecutive operations, prior to the pillaring operation
 itself. These two aspects will be discussed separately.
 Conditioning of the Starting Mica and Vermiculite
 The conditioning treatment consists principally of the reduction of the
 layer charge density of the starting minerals and the replacement of the
 interlayer potassium ions in the initial mica, and of the magnesium ions
 and other cations in the case of vermiculites, by hydrated cations (e.g.
 sodium ions). Conditioning is achieved through the following sequence of
 treatments: the mineral is first treated with diluted mineral acid,
 preferably nitric acid. The solid is washed free of excess acid and
 dissolution products and then calcined at 500-650.degree. C. Thereafter,
 the solid is preferably leached with a diluted (mineral) acid, and
 preferably with a complexing (chelating) organic acid. After elimination
 of the excess complexing agent (or acid) and dissolution debris, the solid
 is converted to the monoionic form by an usual ion-exchange treatment with
 a solution of a soluble salt (e.g. of sodium), and washed free from excess
 salt.
 At this stage, the mineral is ready for the pillaring operation. This
 sequence of treatments is similarly applied to micas and vermiculites (as
 well as to "wastes" thereof, as defined below). The exact conditions of
 acid concentration and treatment duration, however, may differ somewhat
 for a mica and for a vermiculite as it will be illustrated in the
 following examples.
 Pillaring Operation
 The monoionic forms of micas and vermiculites (Na.sup.+, Ca.sup.+2, . . . )
 are contacted with a solution containing the pillaring species (the
 pillaring solution). The pillar precursors are introduced in the
 interlayer space via an exchange process between the charge balancing
 cations of the minerals obtained at the end of the conditioning operation
 and the positively charged species present in the pillaring solution. Any
 known method used for the preparation of pillared smectites may be
 applied.
 Detailed Description of the Conditioning Treatment
 Step 1.--Nitric Acid Treatment
 The starting phlogopite or vermiculite was leached with nitric acid
 solution for 4 hours at 95.degree. C. under stirring, using a
 concentration of solids between 4 and 20 wt %, typically 10 wt %. The
 ratio [mol of nitric acid/mass of phlogopite] was included between 0.007
 and 0.011 mol g.sup.-1, typically 0.008 mol g.sup.-1. The concentration of
 the acid solution ranged between 0.29 M and 1.44 M, typically 0.78 M.
 Step 2.--Thermal Treatment
 The sample obtained at step 1 was calcined at 500-700.degree. C., typically
 at 600.degree. C. for 4 hours under static air.
 Step 3.--Treatment with Complexing Agents (Typically Oxalic Acid)
 The treatment with a complexing agent mainly aims to remove the species
 dissolved from the structure in the preceding steps, which are partly
 present in the interlayers. The conditions were as follows:
 Concentration of solids:
 between 2.6 and 10 wt %, typically 10 wt %
 Concentration of the completing acid solution:
 between 0.06 M and 0.24 M, typically 0.12 M for 10 wt % of solid
 Duration of the treatment:
 micas: between 2.0 and 4 hours, typically 2.5 h
 vermiculites : between 0.5 and 2 hours, typically 1 h
 Temperature of treatment:
 between 80 and 95.degree. C., typically 80.degree. C.
 Alternative (Step-3) treatments:
 Citric Acid
 Sample obtained at step 2 was leached with a 0.5 M citric acid solution (pH
 2.1) at 80.degree. C. for 4 hours.
 Concentration of solids between 1.7 and 4 wt %, typically 4 wt %.
 Acetic Acid
 Sample obtained at step 2 was leached with 0.005 mol acetic acid per gram
 of clay at 80.degree. C. for 3 hours. Concentration of solids of 7.6 wt %.
 Hydrochloric Acid
 Sample obtained at step 2 was leached with 0.0002 mol hydrochloric acid
 peer grain solid at 80.degree. C. for 3 hours. Concentration of solids of
 7.6 wt %.
 Step 4.--Sodium Exchange (*)
 Concentration of the NaCl solution:
 between 1 M and 3 M, typically 1 M.
 Concentration of solids:
 between 0.35 and 6.4 wt %, typically 2 wt %.
 Number of exchange operations:
 between 4 and 6, typically 5 for 12 hours each.
 Temperature of exchange:
 95.degree. C.
 At the end of this step, the exchange sites are occupied by sodium ions.
 Other cationic forms may be obtained by further exchange of the Na-forms
 with solution(s) of the desired element(s).
 (*) Notes:
 Any known cation exchange method may equally be used.
 Any other salt of hydrated cations instead of a Na salt, and different
 concentrations of the exchange solution and exchange times may be used.
 PREFERRED EMBODIMENTS OF THE INVENTION
 1. Pillaring of micas
 Starting phlogopite
 The starting phlogopite-type mica (Siilinjaeervi deposit, Finland) was a
 micronized grade (particle size: 90% smaller than 40 microns, 50% smaller
 than 20 microns). Minor amounts of calcite and apatite were identified by
 X-ray diffraction.
 The chemical analysis (by I.C.P.S.) was as follows (in wt % on the basis of
 samples calcined at 1000.degree. C.).

SiO.sub.2 Al.sub.2 O.sub.3 MgO Fe.sub.2 O.sub.3 K.sub.2 O CaO, NaO,
 TiO.sub.2, P.sub.2 O.sub.5
 41.05 9.71 23.73 7.93 9.50 &lt;6.83
 Step 5.--Pillaring Operation
 The Na-exchanged mica M.sub.4 was dispersed in water (1 wt % of solid), and
 stirred for 24 h (avoided in continuous process). Pillaring was done
 according to existing procedures, as e.g. by slow addition of the
 pillaring solution to the mineral dispersion under stirring while the
 temperature was increased to 80.degree. C. (not indispensable). The volume
 of the Al.sub.13 solution (pillaring solution) was adjusted in order to
 supply a sufficient amount of the pillaring element (12 to 36 mmol Al per
 gram of mica, typically 24 mmol g.sup.-1).
 The contact between the pillaring solution and the solid was maintained for
 4 hours after the end of the addition, at 80.degree. C. (not
 indispensable) under continuous stirring. The solution was eliminated by
 centrifugation and the sample was washed until the conductivity was
 reduced to 0.5 .mu.S cm.sup.-1 1 g.sup.-1 (sample M.sub.5). Sample M.sub.5
 was dried at 60.degree. C. and calcined at the desired temperature for
 characterization purposes.
 Two different Al.sub.13 sources (pillaring solutions) have been used: a
 base (e.g. NaOH) hydrolysed Al solution (e.g. AlCl.sub.3), and a
 commercial solution of Al-chlorhydrol (from Reheis Chem. Co., Ireland).
 a) Pillaring with base hydrolysed Al solution (Typical pillaring solution)
 The pillaring solution was prepared (as in previous works [references
 12-14]) by slow addition of a 0.2 M NaOH solution to a 0.2 M solution of
 AlCl.sub.3, under stirring at 80.degree. C. The required volume of base
 was added to reach an OH/Al molar ratio of 2.4. The Al concentration in
 the final solution was 0.06 M. The solution was aged at room temperature
 for at least 24 h (not indispensable). It has been established that in
 solutions with this molar ratio, about 70-80% of the total aluminium ions
 are present as `Al.sub.13.sup.7+ ` oligocations [references 10, 11-14].
 Notes:
 OH/Al molar ratio is not limited to 2.4 as in the example.
 Al concentration of the pillaring solution is not limited to 0.06 M
 b) Pillaring with commercial Al-chlorhydrol (Reheis Chemical Company,
 Dublin).
 Al-chlorhydrol (or commercial equivalents with trade name PAX and OCAL) is
 formed by the reaction of metal aluminium with aqueous AlCl.sub.3. These
 solutions also contain oligomers larger than Al.sub.13.sup.7+ [reference
 15]. The analysis of the starting Al-chlorhydrol (50% aluminium
 chlorhydrate solution) given by the supplier was as follows:

pH of 30%
 wt % Al.sub.2 O.sub.3 wt % Cl.sup.- Al:Cl atomic ratio Fe (ppm) wt/wt
 sol.
 23.7 8.25 1.96:1 46 4.30
 The commercial solution was diluted to 0.1 M in Al and heated at 60.degree.
 C. for 2 h immediately before use.
 Notes:
 Chlorhydrol may be used either undiluted or at any dilution. Dilution is
 however preferred.
 Heating and ageing of the chlorhydrol solution are not indispensable.
 In the following, "standard method" will refer to the complete sequence of
 operations described above.
 For characterisation purposes, the solids were recovered at the end of the
 different steps described below, washed when necessary and dried
 (superfluous in a continuous preparation procedure).
 Characterisation of Intermediates
 X-ray Diffraction Data
 The spacings corresponding to the (001) reflection were determined from
 X-ray diffraction patterns recorded with a Philips type PW 1130-90
 instrument (CoK.alpha. radiation, Fe-filtered) or a Siemens D-5000
 diffractometer (CuK.alpha. radiation, Ni-filtered). The scanning rate was
 1.degree. 2.theta. min.sup.-1. The spacings of intermediates are given in
 Table 1.
 Sample M.sub.1 (treated with nitric acid, washed and dried at 60.degree.
 C.):
 Three peaks appeared in the low angle region, one with spacing of 10.1
 .ANG. (starting phlogopite), and two new peaks at d=25 .ANG. (absent in
 the starting mica) and at 11.6 .ANG.. After calcination at 500.degree. C.,
 only the peak at 10.1 .ANG. remained.
 Sample M.sub.2 :
 After calcination of M.sub.1 at 600.degree. C., only one peak remained at
 10 .ANG..
 Sample M.sub.3 :
 Spacing analogous to that of M.sub.2
 Sample M.sub.4 :
 Suitable Na-exchange was characterised by the expansion of the basal
 spacing to 12.2 .ANG. at 60.degree. C. (another peak with d=14.5 .ANG. was
 observed in higher humidity conditions). Na-exchange was confirmed by the
 contraction of the basal spacing to 9.7 .ANG. after heating at 500.degree.
 C.
 TABLE 1
 XRD data: interplanar distances (in .ANG.)
 Sample At room temperature At 500.degree. C.
 M.sub.i 10.1 10.1
 M.sub.1 25, 11.7-11.5, 10.1 10.0
 M.sub.2 10.0-10.15 --
 M.sub.3 10.1-10.25 10.05
 M.sub.4 12.2, (14.5) 9.7
 M.sub.5 18.5, (14.1-13.8)* 18.3-17.7
 *: very weak intensity
 Textural Characteristics
 The surface areas (S.sub.BET) were obtained by applying the BET treatment
 to the nitrogen sorption isotherms measured at 77K (ASAP 2000 Sorptometer,
 from Micromeritics) in the domain of relative pressures of 0.05-0.25, on
 samples previously outgassed for 6 h at 200.degree. C. The total pore
 volumes (Vo) were established from the amount of nitrogen adsorbed at a
 relative pressure of 0.985, and the micropore volumes (V.mu.) were
 calculated by the `t-plot` method [reference 16].
 The experimental values are given in Table 2. The Na-exchanged sample
 (M.sub.4) showed almost no microporosity, and a small increment of the
 surface area and the total pore volume with respect to the starting
 mineral (M.sub.i).
 TABLE 2
 Textural characteristics of samples calcined at 500.degree. C.. BET
 specific
 surface area (S.sub.BET), total pore volume (V.sub.0) and micropore
 volume (V.sub..mu., t-plot method).
 S.sub.BET V.sub.0 V.sub..mu.
 Sample m.sup.2 g.sup.-1) (cm.sup.3 g.sup.-1) (cm.sup.3 g.sup.-1)
 M.sub.i 2 0.010 0.000
 M.sub.4 28 0.067 0.000
 An illustration of the complete N.sub.2 isotherms of M.sub.i and M.sub.4
 (outgassed at 200.degree. C.) is shown in FIG. 1.
 During the conditioning step, the particle size (measured with a Coulter
 LS130 apparatus) was almost unchanged in the medium and small size part of
 the distribution curve. A diminution of the size of the larger fraction
 was noticed, as shown in Table 3.
 TABLE 3
 Particle size analysis (0.1 .mu.m-900 .mu.m)
 Size (.mu.m) Size (.mu.m) Size (.mu.m)
 Sample Mode (.mu.m) 90%&lt; 50%&lt; 10%&lt;
 M.sub.i 67 277 59 17
 M.sub.4 61 110 50 16
 Other Characteristics
 The cation exchange capacity (CEC) of M.sub.4, determined by micro-Kjeldahl
 analysis on an ammonium-exchanged sample, was 1.46 meq g.sup.-1.
 The .sup.27 Al MAS-NMR spectrum of the starting mica (Mi in FIG. 2)
 (recorded with a Bruker 400 MSL spectrometer; magnetic field of 9.4 T;
 pulse length of 0.6 .mu.s; tipping angle of 10.degree.; recycle delay of
 0.1 s; spinning rate of the 4 mm diameter rotor: 12 kHz; number of scans:
 3000) showed a signal at 63 ppm, characteristic of tetrahedral aluminium.
 After acid leaching (spectrum M1), there is a decrease of the signal at 63
 ppm and a new signal appears at around 0-3 ppm, indicating that part of
 the tetrahedral Al has been converted to extraframework octahedral Al. The
 signals at 190 ppm and -60 ppm are side bands associated to the main
 signal at 63 ppm. After carrying out step 2 (spectrum M2), the signal at
 0-3 ppm is much reduced and slightly shifted to 10 ppm. It has almost
 totally disappeared after the sodium exchange (spectrum M4). The spectrum
 of the Al-pillared mica (M5) exhibits an intense signal at about 0 ppm,
 typical of octahedral Al of the pillars. The two signals at about 140 and
 -120 ppm are side bands associated with that at 0 ppm.
 Characterization of Al-pillared micas
 Sample M.sub.5 :
 After treatment with the pillaring solution, intercalation of the Al.sub.13
 species was evidenced by the expansion of the spacing to 18.7-18.5 .ANG..
 A minor fraction of the mica was intercalated with smaller aluminium
 species (mainly monomeric aluminium), characterised by a diffraction peak
 at 14.1-13.7 .ANG..
 Heating M.sub.5 at 500.degree. C. resulted in a limited contraction due to
 dehydration-dehydroxylation of the pillar precursor (Keggin-type cation)
 to the corresponding pillar oxide. This contraction was shown by a small
 shift of the 001 reflection from 18.5 .ANG. to 18.3-17.7 .ANG., depending
 on the calcination conditions, while the minor fraction intercalated with
 monomeric species collapsed to 10.5 .ANG.. These changes are summarized in
 Table 1.
 Thermal stability, textural and structural characteristics (Al-pillared
 micas)
 The DTG curve (obtained with a Setaram TG-DTA 92 thermobalance in dynamic
 air atmosphere and heating rate of 10.degree. C. min.sup.-1) showed that
 adsorbed water is removed at 150.degree. C. A continuous weight loss
 occurred between 150 and 500.degree. C. associated with the
 dehydroxylation of the OH ligands of the aluminium pillars.
 Dehydroxylation of the mica structure occurred at 800-850.degree. C. The
 total weight loss (60-1000.degree. C.) was 22.2%.
 The textural characteristics established from the nitrogen sorption
 isotherms are given in Table 4. The micropore volumes of the pillared
 micas were determined according to a method described in [reference 17].
 The specific surface areas and the micropore volumes remain nearly constant
 after calcination up to 600.degree. C. and keep high values even at
 700.degree. C. A noticeable decrease of the surface area and microporous
 volume is observed after calcination at 800.degree. C. At 850.degree. C.
 and above, the structural identity of the pillared material is lost.
 TABLE 4
 Textural characteristics of pillared samples after calcination.
 (heating rate: 1.degree. C. min.sup.-1 with a plateau of 2 h at the final
 temperature; outgassing at 200.degree. C. under 10.sup.-4 Torr)
 S.sub.BET V.sub.0 V.sub..mu.
 Sample (m.sup.2 g.sup.-1) (cm.sup.3 g.sup.-1) (cm.sub.3
 g.sup.-1)
 M.sub.5 -RT (batch 2) 356 0.220 0.129
 M.sub.5 -RT (batch 1) 351 0.250 0.123
 M.sub.5 -400 (batch 2) 339 0.201 0.114
 M.sub.5 -500 (batch 1) 365 0.268 0.119
 M.sub.5 -600 (batch 2) 339 0.201 0.114
 M.sub.5 -700 (batch 1) 283 0.153 0.094
 M.sub.5 -800 (batch 1) 145 0.073 0.036
 The complete N.sub.2 adsorption-desorption isotherms of Al-pillared
 phlogopite established after calcination at increasing temperatures are
 shown in FIG. 1 (M.sub.5 -500, M.sub.5 -700 and M.sub.5 -800).
 The structural changes follow a similar tendency, namely, a relatively
 slight diminution of the basal spacing after calcination at
 400-600.degree. C. But even at 800.degree. C., the spacing remains quite
 high (see Table 5).
 TABLE 5
 Basal spacings (in .ANG.) of M.sub.5 after calcination for 2 h at
 increasing
 temperatures (heating rate: 1.degree. C. min.sup.-1 ; plateau of 2 h at the
 final temperature).
 T(.degree. C.) 60 400 500 600 700 800 850
 d.sub.001 18.7 18.3 17.7 17.4 16.2 16.0 12.7
 The limit of the thermal stability was 840.degree. C. (from DTA curve).
 The acid content of Al-pillared phlogopite M.sub.5 calcined at 500.degree.
 C. (determined by adsorption of ammonia at 100.degree. C. followed by
 temperature-programmed desorption (TPD) of ammonia between 100 and
 550.degree. C.) was 0.29 meq g.sup.-1.
 Intercalation of Al.sub.13 was confirmed by .sup.27 Al MAS NMR
 spectroscopy. The spectrum showed an increase of the signal at 63 ppm
 corresponding to structural Al and to Al of the pillars, both in fourfold
 coordination, and a new signal at 3-4 ppm characterizing Al in octahedral
 coordination originating from the pillars.
 This is illustrated in FIG. 2 which compares the spectra obtained for the
 starting mica (1), after Na-exchange (2), and after pillaring (3). The
 signals showing up above 100 ppm and below -20 ppm are side bands.
 Variation of Some Preparation Parameters
 Table 6 compiles the textural characteristics, namely the specific surface
 areas (S.sub.BET), the micropore volumes [method of reference 17]
 (V.sub..mu.), and the total pore volumes (Vo) of M.sub.5 solids in
 relation with the conditions employed at each step.
 All these pillared samples calcined at 500.degree. C. showed basal spacings
 between 17.4 .ANG. to 18 .ANG..
 TABLE 6
 Textural parameters of selected samples (not typical conditions)
 S.sub.BET V.sub..mu.
 V.sub.0
 Sample step 1 step 2 step 3 step 4 step 5 m.sup.2 g.sup.-1 cc
 g.sup.-1 cc g.sup.-1
 M.sub.5 -500 0.29 500 citric 6 .times. 1M lab-12 228 0.086
 0.147
 M.sub.5 -600 0.29 500 citric 6 .times. 1M lab-12 222 0.073
 0.146
 M.sub.5 -700 0.29 500 citric 6 .times. 1M lab-12 218 0.074
 0.137
 M.sub.5 -500 0.29 500 ox 5 .times. 1M lab-12 287 0.083
 0.165
 M.sub.5 -500 1.44 500 ox' 5 .times. 1M lab-24 261 0.097
 0.191
 M.sub.5 -700 1.44 500 ox' 5 .times. 1M lab-24 237 0.080
 0.181
 M.sub.5 -500 1.44 500 ox' 4 .times. 1M lab-12 261 0.089
 0.193
 M.sub.5 -500 1.44 500 ox' 4 .times. 3M lab-12 237 0.079
 0.163
 M.sub.5 -500 0.72 500 ox" 5 .times. 1M lab-12 279 0.105
 0.186
 M.sub.5 -500 0.72 h500 ox" 5 .times. 1M lab-12 234 0.086
 0.155
 M.sub.5 -200 0.29 500 ox 5 .times. 1M lab-36 310 0.115
 0.210
 M.sub.5 -500 0.29 500 ox 5 .times. 1M lab-36 264 0.094
 0.193
 M.sub.5 -600 0.29 500 ox 5 .times. 1M lab-36 267 0.083
 0.200
 M.sub.5 -400/1 0.78 500 ox' 3 .times. 3M Chlr-24 196 0.025
 0.153
 Step 1
 Column entitled "step 1" gives the molar concentration (M) of the nitric
 acid solution.
 The concentration of solids was 3 wt % for 0.29 M nitric acid; 10 wt % for
 0.72 M and 0.78 M; and 20 wt % for 1.44 M (constant mol H.sup.+ g.sup.-1
 solid=0.007).
 Step 2
 Column "step 2" shows the heating temperature; h meaning no drying prior to
 thermal treatment.
 Step 3
 Column "step 3" gives a code related to the nature of the complexing
 solution, time and temperature used. The meaning of the code is the
 following: ox: 0.06 M oxalic acid, 4 h, 80.degree. C.; ox': 0.12 M oxalic
 acid, 3 h, 80.degree. C.; ox": 0.06 M oxalic acid, 3 h, 95.degree. C.
 Step 4
 This column refers to the number of ion exchange operations performed
 (renewals of the exchange solution); xM refers to the molarity of the NaCl
 solution.
 Step 5
 Column "step 5" indicates the type of pillaring solution:lab: prepared by
 base-hydrolysis of AlCl.sub.3 solution (OH/Al=2.4); Chlr: commercial
 Chlorhydrol; -12 and -24 stand for the amount of Al supplied per g
 mineral, respectively, 12 and 24 mmol Al g.sup.-1 clay.
 Calcination in mufle oven (heating rate: 12-13.degree. C. min.sup.-1).
 Note: Trials using at step 3 acetic and hydrochloric acid in place of
 oxalic or citric acid gave as well pillared micas with c.a. 18 .ANG.
 spacings (samples calcined at 500.degree. C.). At the difference with
 samples treated with the preferred acids, the X-ray pattern exhibited a
 second reflection at 14 .ANG. (room temperature drying) which was more
 significant than in samples using oxalic or citric acid, but less
 important than when step 3 was omitted.
 The intensity ratios of the 18 .ANG. phase to the 14 .ANG. phase in samples
 treated with acetic acid, hydrochloric acid, and when omitting step 3 in
 samples dried at room temperature were, respectively, 3.6, 3.1 and 2.0,
 and increased to 16, 15 and 9 respectively after calcination at
 500.degree. C., thus showing that acetic acid and hydrochloric acid may
 also be used at step 3.
 2. Al-Pillaring of Vermiculites
 Venmiculites from Palabora Company (South Africa) and Libby (Montana)
 deposit were treated following the "standard method" and characterised.
 Starting Vermiculites
 The vermiculite from Palabora Company was superfine grade and it is noted
 as P.sub.i. The vermiculite from Libby (Montana) deposit is noted as
 L.sub.i.
 The C.E.C. determined on Ba-exchanged P.sub.i was 1.85 meq g.sup.-1
 The chemical analyses obtained by I.C.P.S. for P.sub.i and L.sub.i are
 given in Table 7 (in wt %):
 TABLE 7
 Chemical analysis data (wt %) on basis of samples calcined at 1000.degree.
 C.
 SiO.sub.2 Al.sub.2 O.sub.3 Fe.sub.2 O.sub.3 MgO CaO K.sub.2 O
 F.sup.- L.I.
 P.sub.i 43.3 9.3 8.6 24.1 5.1 4.8 0.9 11.1
 L.sub.i 41.2 9.2 6.8 28.3 3.3 4.6 0.2 12.6
 L.I.: weight loss on ignition at 1000.degree. C.
 Pillared vermiculites were prepared according to the sequence of treatments
 described for the mica. Palabora and Libby vermiculites will be
 distinguished by, respectively, P (P.sub.1 to P.sub.5) and L (L.sub.1 to
 L.sub.5). The experimental conditions employed at the various steps are
 indicated hereafter.
 Conditioning and pillaring conditions

Step 5:
 Pillaring solution OH/Al = 2.4
 mmol Al/g solid 24
 contact time (h) 4
 temperature (.degree. C.) 80
 Samples P.sub.5 and L.sub.5
 Characteizadon of Conditioning Intermediates (P.sub.i to P.sub.4, L.sub.i
 to L.sub.4)
 X-ray Diffraction Data
 The spacings of the samples dried at room temperature and calcined at
 500.degree. C. at the different steps are given in Table 8.
 TABLE 8
 Basal spacings (in .ANG.) of samples dried at room temperature
 and calcined at 500.degree. C.
 Sample Room T (.ANG.) 500.degree. C. (.ANG.)
 P.sub.i 24.5, 14.2, 12.4, 11.8 25, 14, 11.5, 9.9
 P.sub.1 24.7, 11.9 9.8
 P.sub.2 9.8-10.0
 P.sub.3 9.8-10.25 9.9
 P.sub.4 12.2-12.4 9.7-9.65, (12.2)*
 L.sub.i 25, 12.6, 12.0 24.9, 12, 10.15
 L.sub.1 25, 12.0 9.8
 L.sub.2 10.0
 L.sub.3 10.0-10.2 10.0-10.2
 L.sub.4 12.2-12.4, (13.6) 9.7-9.65, (12.2)*
 *partial rehydration
 The Na-exchange (P.sub.4, L.sub.4) was confirmed by the spacing of 12.2
 .ANG. at room temperature (hydrated form) collapsing to 9.65-9.7 .ANG.
 after heating at 500.degree. C.
 Textural Characteristics
 The Na-exchanged samples (P.sub.4, L.sub.4) outgassed at 200.degree. C. for
 6 h (Table 9) show no microporosity, and an increment of the surface area
 and of the total pore volume with respect to the starting vermiculite
 (P.sub.i). The nitrogen sorption isotherms corresponding to P.sub.1 and
 P.sub.4 are shown in FIG. 3.
 TABLE 9
 Textural characteristics
 Specific surface area (S.sub.BET), total pore volume (V.sub.0) and
 micropore volume (V.sub..mu.) (t-plot method) of samples precalcined at
 500.degree. C.
 S.sub.BET V.sub.0 V.sub..mu.
 Sample (m.sup.2 g.sup.-1) (cm.sup.3 g.sup.-1) (cm.sup.3 g.sup.-1)
 P.sub.i 2 0.004 0.000
 P.sub.4 43 0.074 0.001
 L.sub.4 22 0.036 0.000
 Particle Size Analysis
 The analysis data of sample P4 are compared with those of the starting
 vermiculite in Table 10. As in the case of micas, a reduction of the
 particle size occurs during the conditioning steps.
 TABLE 10
 Particle size analysis (0.1 .mu.m-900 .mu.m)
 Size (.mu.m) Size (.mu.m) Size (.mu.m)
 Sample 90%&lt; 50%&lt; 10%&lt;
 P.sub.i (superfine) 819 515 22
 L.sub.i 684 290 74
 P.sub.4 252 102 32
 Other Characteristics
 The CEC (cation exchange capacity) prior to pillaring (P.sub.4) was 1.32
 meq g.sup.-1 (micro-Kjeldahl method on ammonium-exchanged form). Note: The
 starting vermiculites (P.sub.i, L.sub.i) may be directly converted in any
 desired homoionic form without proceeding to steps 1 to 3. However,
 pillaring cannot be achieved without these steps.
 Characterization of Al-pillared Vermiculites
 Textural and Structural Characteristics
 The textural results derived from the nitrogen sorption isotherms of sample
 P5 (uncalcined and previously calcined at different temperatures with
 heating rate of 1.degree. C. min.sup.-1) are given in Table 11. Prior to
 the sorption measurements, the samples were outgassed at 200 .degree. C.
 for 6 h.
 TABLE 11
 Textural characteristics.
 BET specific surafce area (S.sub.BET), total pore volume (V.sub.0) and
 micropore volume (V.sub..mu.) of samples calcined at increasing
 temperatures
 S.sub.BET V.sub.0 V.sub..mu. *
 Sample (m.sup.2 g.sup.-1) (cm.sup.3 g.sup.-1) (cm.sup.3 g.sup.-1)
 P5-200 (Na) 296 0.185 0.098
 P5-400 (Na) 307 0.192 0.109
 P5-500 (Na) 322 0.215 0.120
 P5-600 (Na) 241 0.166 0.071
 P5-700 (Na) 216 0.144 0.068
 P5-400 (Ca) 291 0.197 0.112
 P5-500 (Ca) 318 0.211 0.119
 P5-600 (Ca) 326 0.215 0.123
 P5-700 (Ca) 226 0.159 0.082
 P5-800 (Ca) 184 0.138 0.062
 L5-400 (Ca) 241 0.158 0.083
 L5-600 (Na) 212 0.142 0.071
 *Method of [reference 17]
 The textural characteristics obtained on Palabora vermiculite, exchanged,
 at step 4, with a calcium salt instead of a sodium salt, both homoionic
 forms being pillared as indicated above, are compared in Table 11. The use
 of a Ca salt at the step 4 improves the characteristics of the pillared
 material at similar calcination temperatures.
 The complete nitrogen adsorption-desorption isotherms of P5 calcined at
 400.degree. C. and 700.degree. C. are shown as example in FIG. 3
 As seen in Table 12, after treatment with the pillaring solution, the
 intercalation of the Al.sub.13 is confirned by the expansion of the
 interlayer distance to 18.7-18.2 .ANG.. A minor fraction of the
 vermiculite was intercalated with smaller aluminium species (mainly
 monomeric aluminium) with spacings of 14.1-13.7 .ANG.. At 400.degree. C.,
 the spacing was somewhat reduced (18.4 .ANG.) and the minoritary fraction
 intercalated with monomeric species collapsed to 10.5 .ANG.. No
 significant difference was noticed according to the cation species
 exchanged at step 4.
 FIG. 4 shows the XRD diffraction patterns of the Al-intercalated Palabora
 vermiculite, aflter drying at 60.degree. C. and subsequent calcination at
 increasing temperatures (in the same conditions as above).
 TABLE 12
 Basal spacing d001 (.ANG.) of pillared vermiculites (Samples
 calcined at heating rate of 1.degree. C./min; plateau maintained for 2 h).
 T (.degree. C.) 60 400 500 600 700 800
 P5 (Na) 18.7 18.4 18.2-17.7 17.2 16.4 16.3
 P5 (Ca) 18.7 18.2 17.7 17.2 16.7 16.0
 L5 (Na) 18.7 18.2 17.8 17.5 16.6 --
 3. Al-Pillaring of Precalcined Vermiculites
 Starting Vermiculite
 Exfoliation of vermiculite is done by feeding crude vermiculite at
 controlled rate in a vertical furnace heated at 800-1000.degree. C. The
 residence time is of the order of a few seconds, during which the
 hydration water around the charge balancing cation (Mg.sup.2+) is
 instantaneously vaporized. Due to high local steam pressure in the
 interlayers, flash expansion of the vermiculite platelets occurs, with a
 ten- to twenty-fold expansion of the platelets, resulting in low density
 multilayer particles. These exfoliated vermiculites are employed e.g. for
 their thermal insulating properties. Separation of the fines is done e.g.
 by cyclonisation. These fines are not recycled (wastes).
 The fine fraction of Palabora vermiculite with mean particle size of 50
 .mu.m recovered after the cyclonisation step will be referred to hereafter
 as "precalcined vermiculite" (previously named `wastes`). Small amounts of
 calcite and possibly biotite were identified by X-ray diffraction. The
 experiments were done on the as received sample, without grinding and
 fractionation treatments.
 The cation exchange capacity (CEC) of the starting sample was 0.48 meq
 g.sup.-1, namely, about three times less than normal value found for crude
 trioctahedral vermiculites (example II). This low value is probably
 related to the previous flash treatment at 800.degree. C. The starting
 vermiculite will be noted as V.sub.i.
 Conditioning of the Precalcined Vermiculite
 Conditioning consisted of submitting the starting vermiculite to a similar
 sequence of treatments (standard method) as that for micas and crude
 (uncalcined) vermiculites. The conditions were as follows:
 Step 1:
 The starting vermiculite was treated with a 0.23 M solution of nitric acid
 at 95.degree. C. for 4 h and under continuous stirring, using 25 ml of the
 acid solution per gram of vermiculite. The acid-leached solid was
 thoroughly washed and dried at 60.degree. C. (Sample V.sub.1 hereinafter).
 Step 2
 Solid V.sub.1 was calcined at 600.degree. C. for 4 h under static air
 (sample V.sub.2).
 Step 3
 Sample V.sub.2 was leached for 4 h at 80.degree. C. under continuous
 stirring with a 0.5 M citric acid solution (pH=2.1) using 40 ml g.sup.-1
 of solid. The solid was washed free from excess acid and salts, and dried
 at 60.degree. C. (sample V.sub.3).
 Step 4
 Solid V.sub.3 was treated 5 times (for 12 h each) with a 1 M sodium
 chloride solution (50 ml g.sup.-1 of solid). The exchange operation was
 preferably carried out at 95.degree. C. under continuous stirring. The
 solid recovered was washed and dried at 60.degree. C. (sample V.sub.4).
 At the end of this four steps treatment, the Na-exchanged vermiculite was
 ready for the pillaring operation. Note that at step 4, the Na-vermiculite
 may be converted via any usual exchange method to any desired cationic
 form.
 Al-pillaring of Precalcined Vermiculite
 The Na-exchanged vermiculite obtained at the end of step 4 (sample V.sub.4)
 was dispersed in water (0.5 wt % of solid) and the suspension was stirred
 for 24 h (unnecessary in a continuous procedure). The Al-pillaring
 solution (base hydrolyzed AlCl.sub.3, with OH/Al molar ratio of 2.4) was
 slowly added under stirring to the vermiculite dispersion, adding a
 sufficient volume to supply 12 mmol Al g.sup.-1 vermiculite.
 After addition of the pillaring solution, the final suspension was aged for
 4 h at 80.degree. C. under stiring. The suspension was centrifuged and the
 solid was washed and dried at 60.degree. C. (sample noted V.sub.5). The
 dried sample was then calcined for two hours at 500 and 700.degree. C.,
 using a heating rate of 13.degree. C./min.
 Characterization of Intermediates (Samples V.sub.1 to V.sub.4)
 The solids obtained at each separate step were characterised with the same
 techniques and methods as for the preceding examples. As mentioned earlier
 (in examples I and II), in the continuous preparation process, namely,
 from the starting vermiculite (V.sub.i) to its Al-pillared form (V.sub.5),
 intermediate dryings are omitted.
 The main observations concerning the solids obtained at the end of steps 1
 to 4 are summarised hereafter. The characterisation of the Al-pillared
 vermiculite (V.sub.5) will be treated separately.
 X-ray Diffraction
 The basal spacings of samples (previously calcined for 2 h at 500 .degree.
 C.) obtained at the end of steps 1 to 4 are given in Table 13.
 TABLE 13
 Basal spacings (in .ANG.) at 500.degree. C.
 V.sub.i 10.15
 V.sub.1 10.1
 V.sub.2 10.1 (600.degree. C.)
 V.sub.3 10.15
 V.sub.4 9.7 (12.1)
 The diffraction pattern of the starting vermiculite (V.sub.i) exhibited
 reflections of hydrated vermiculite (peak at 14.5 .ANG.), biotite (10.1
 .ANG.) and interstratified, R=1, biotite-venniculite with interplanar
 distances of 25.2 and 12.2 .ANG..
 After acid leaching and calcination at 500.degree. C. (V.sub.1 -500), the
 interstratified phase disappeared and a single reflection at 10.1 .ANG.
 with a much increased intensity was noticed.
 The X-ray patterns of the samples V.sub.2 (thermal treatment) and V.sub.3
 (citric acid leaching) did not exhibit significant modification with
 respect to that of calcined V.sub.1.
 A small but qualitatively important decrease of the basal spacing was
 noticed for the Na-exchanged vermiculite (V.sub.4 -500), with a
 contraction of 0.3-0.4 .ANG., indicative of total exchange. Partially
 Na-exchanged samples exhibited, after calcination at 500.degree. C., peaks
 corresponding to interplanar distances of 10.1 and 9.9 .ANG..
 As it will be illustrated below, well pillared vermiculites were only
 obtained from thoroughly exchanged Na-vermiculite, as for the preceding
 examples.
 Cation Exchange Capacity
 After treatment with nitric acid (sample V.sub.1) the cation exchange
 capacity increased from 0.48 (V.sub.i) to 1.49-1.50 meq g.sup.-1. Treating
 vermiculite in step 1 with nitric acid (0.23 M at 95.degree. C. for 4 h)
 or citric acid (0.5 M at 80.degree. C. for 4 h) gave solids with identical
 CECs.
 After calcination at 600.degree. C. (sample V.sub.2), the CEC decreased
 from 1.50 to 1.11 meq g.sup.-1 (a loss of about 26%).
 Removal of the interlayer species upon treatment with citric acid (sample
 V.sub.3) resulted in an increase of the CEC, from 1.11 to 1.23 meq
 g.sup.-1. The initial value of 1.50 meq g.sup.-1 was not restored, which
 indicates a reduction of the overall negative charge.
 Textural Properties
 The nitrogen adsorption-desorption isotherms at 77K of the starting
 (V.sub.i -500) and Na-exchanged vermiculites (V.sub.4 -500), shown in FIG.
 5, correspond to type IV of the IU classification, characteristic of
 mesoporous solids, with a H3-type hysteresis loop, generally encountered
 for (layered) lamellar minerals [reference 18].
 The textural characteristics of samples V.sub.i to V.sub.4 are indicated in
 Table 14.
 TABLE 14
 Textural parameters of selected samples
 S.sub.BET V.sub..mu. V.sub.0
 Sample (m.sup.2 g.sup.-1) (cm.sup.3 g.sup.-1) (cm.sup.3 g.sup.-1)
 V.sub.i 11 0.000 0.031
 V.sub.1 68 0.008 0.097
 V.sub.2 20 0.001 0.057
 V.sub.2-Na 17 0.001 0.050
 V.sub.4 30 0.001 0.086
 V.sub.5' -500 153 0.056* 0.121
 V.sub.5 -500 192 0.066* 0.177
 V.sub.5 -500 179 0.065* 0.150
 V.sub.5 -700 121 0.041* 0.118
 *method of [reference 17]
 As shown in Table 14, the treatment with nitric acid enhances the external
 surface area, from 11 m.sup.2 g.sup.-1 (untreated vermiculite, V.sub.i) to
 68 m.sup.2 g.sup.-1 (V.sub.1) mainly attributable to the increase of the
 macropore volume. Micropores are almost absent.
 The thermal treatment (sample V.sub.2) provoked a diminution of the
 specific surface area, from 68 to 20 m.sup.2 g.sup.-1.
 The nitrogen sorption isotherms established on samples V.sub.2 (not shown)
 and V.sub.4 did not exhibit marked differences. The specific surface area
 of the vermiculite subsequently leached with citric acid (step 3) and
 Na-exchanged (step 4) was 30 m.sup.2 g.sup.-1 (V.sub.4 in Table 14), thus
 only slightly higher.
 Characterization of Al-pillared Precalcined Vermiculites
 X-ray Diffraction Analysis
 The pillaring step is of course the one which leads to the obtention of
 pillared vermiculite and, according to whether a 18 .ANG. phase (at room
 temperature) is achieved or not, it constitutes somehow an `enlightener`
 on whether the intermediate steps were or were not properly conducted.
 FIG. 6 shows the XRD patterns of V.sub.5 after calcination between 500
 .degree. C. and 700.degree. C. The basal spacings of selected samples
 after calcination are given in Table 15.
 TABLE 15
 Basal spacings (in .ANG.)
 Sample Spacing (.ANG.)
 V.sub.5' -500 (without step 3) 17.6-17.7
 V.sub.5 -500 17.6-17.7
 V.sub.5 -600 16.4
 V.sub.5 -700 16.3
 Al-pillared vermiculite exhibited a basal spacing of 18.6 .ANG. for sample
 dried at room temperature, and 17.6 .ANG. after calcination at 500.degree.
 C. (Table 15). Similar spacings were found for Al-pillared micas and
 Al-pillared crude vermiculite.
 Pillared and Al-exchanged phases can be easily distinguished on the XRD
 patterns. In order to evaluate the quality of the pillared materials, the
 ratio between the peak height of the 001 reflection of the pillared phase
 (ca. 17.6 .ANG. at 500 .degree. C.) and that of the peak corresponding to
 the Al-exchanged vermiculite (peak at 10.5 .ANG. at 500.degree. C.), in
 short as I.sub.18 /I.sub.10, is used, after background subtraction. For
 instance, there was a substantial increase of the peak intensity ratio
 (I.sub.18 /I.sub.10) when the material obtained at the end of step 2 was
 treated with citric acid (I.sub.18 /I.sub.10 =7-11) compared with a sample
 which was not treated (I.sub.18 /I.sub.10 =3.1).
 Thermal Stability
 Pillared vermiculite calcined at 500.degree. C. had a spacing of 17.6-17.5
 .ANG. (Table 15) which decreased to 16.4 and 16.3 .ANG. after calcination
 at 600 and 700.degree. C. respectively. The decreasing interplanar
 distances are similar to those observed for pillared micas.
 Thermogravimetry (TGA, DTG)
 The pillaring of vermiculite was confirmed by TGA data. The Al-pillared
 V.sub.5 sample showed between 60 and 300.degree. C., a weight loss about
 twice as much as for V.sub.4 (Na-vermiculite). The further loss of the OH
 ligands of the pillars was indicated by a DTG minimum at 515.degree. C.
 The structural dehydroxylation of the vermiculite occurred at 835.degree.
 C. The total weight loss between 60 and 1050.degree. C. of the Al-pillared
 vermiculite amounted to 16.42%, compared with 7.1 and 9.46% for,
 respectively, V.sub.i and V.sub.4.
 Textural Characteristics
 N.sub.2 adsorption-desoiption isotherms were established on pillared
 samples before and after calcination at 500.degree. C. As in the case of
 pillared smectites (PILCs) and pillared micas (PILMs), intercalation of Al
 pillars between the layers is accompanied by the development of
 microporosity.
 As seen in Table 14, the BET surface area of samples calcined at
 500.degree. C. increased from 30 m.sup.2 g.sup.-1 before pillaring (sample
 V.sub.4) to 179-192 m.sup.2 g.sup.-1 for a sample which was previously
 treated with citric acid (V.sub.5 '-500), or to 153 m.sup.2 g.sup.-1 when
 the citric acid leaching (step 3) was omitted (V.sub.5 '-500). This
 increase of the surface area is directly related to the development of
 microporosity.
 Residual CEC and Acid Content
 The residual CEC (V.sub.5 -500) obtained for a pillared vermiculite was
 0.27 meq g.sup.-1. A value of 0.29 meq g.sup.-1 was obtained for
 Al-pillared micas.
 The acid content (temperature-programmed desorption of ammonia between 100
 and 550.degree. C.) gave an average value of 0.20 mmol g.sup.-1.
 MAS-NMR Spectroscopy
 The .sup.27 Al MAS-NMR spectrum of V.sub.4 showed only one signal at 63 ppm
 corresponding to structural tetrahedral aluminium (aluminium in the
 tetrahedral layers). The Al-pillared sample (V.sub.5 -500) exhibited two
 signals at 3-5 ppm, typical for octahedral Al, and at 63 ppm,
 characteristic of tetrahedral Al. The signal near 5 ppm corresponds to
 Al.sup.VI (octahedral Al) of the pillars and the one at 63 ppm is the
 superimposition of the signal of Al.sup.IV (tetrahedral Al) of the pillars
 and Al in the tetrahedral layers of vermiculite.
 Alternative Conditioning Treatments Investigated
 In order to have a better insight into the role of each one of the
 different steps of the standard method, several alternatives have been
 examined. To check the effect of those variables on pillaring, XRD is the
 most adequate technique because it permits to identify the phases in
 presence and give an evaluation of their relative proportions.
 Successful pillaring is evidenced by the absence of unpillared fraction
 (X-ray diffraction peak at 10.1 .ANG. after calcination of the sample at
 500.degree. C.) after the pillaring treatment. Intercalation of Al.sub.13
 -type species should be favoured with respect to exchange with monomeric
 aluminium. The I.sub.18 /I.sub.10 ratio, as defined above, ranged between
 0.5, for very poorly pillared vermiculites, and 7 and higher for well
 pillared materials in the case of precalcined vermiculite.
 Some results of additional trials investigated (summarized in Table 16) are
 briefly described hereafter and commented altogether. Step 3 (citric acid
 treatment) when not specifically targeted has been omitted because it was
 not indispensable to verify suitable pillaring of the material. In doing
 so, a more rapid information on the influence of the modified parameters
 can be obtained. However, better pillared materials are obtained when
 carrying out step 3.
 TABLE 16
 Main alternatives investigated.
 Trial Step 1 Step 2 Step 3 Step 4
 n1 HNO.sub.3 0.17M ////////
 HNO.sub.3 0.25M ////////
 HNO.sub.3 0.46M ////////
 n2 citric ////////
 n3 HCl ////////
 n4 /////////// ////////
 n5 HNO.sub.3 H.sub.2 O steam ------------
 n6 HNO.sub.3 //////// ////////
 n7 HNO.sub.3 ////////
 n8 HNO.sub.3 ////////
 HNO.sub.3 NH.sub.4.sup.+
 //////// means step not performed
 Trials related with step 1. Effect of acid concentration
 Run 1.
 In distinct experiments, acid treatment in step 1 has been performed with,
 respectively, 0.17 [0.006 mole H.sup.+ g.sup.-1 ], 0.25 [0.009 mole
 H.sup.+ g.sup.-1 ], and 0.46 [0.016 mole H.sup.+ g.sup.-1 ] M nitric acid
 solutions, keeping constant the solid concentration (thus changing the mol
 H.sup.+ g.sup.-1 solid ratio), the leaching temperature and duration of
 the treatment being as in the "standard" procedure, and steps 2, 4, and 5
 being subsequently carried out according to the standard procedure.
 Pillaring was better achieved when vermiculite was treated with 0.009 mole
 nitric acid per gram solid. Using either higher or lower acid
 concentration resulted in poorer pillared materials. The best results were
 obtained when vermiculite was treated with a quantity of acid of about
 five to six times the CEC of the vermiculite; higher acid concentrations
 provoked irreversible structural damage, resulting in nonpillarable
 materials.
 Influence of Type of Acid (Runs 2 and 3)
 Run 2.
 Substituting citric acid for nitric acid in step 1, in other words carrying
 out step 3 instead of step 1, followed by steps 2, 4 and 5, resulted in
 very poorly pillared material (I.sub.18 /I.sub.10 ratio=0.6), suggesting
 that steps 2 to 5 did not operate as in the "standard" procedure.
 Run 3.
 Substitution of hydrochloric acid or sulfuric acid for nitric acid with
 similar concentration (steps 2, 4 and 5 being carried out as in the
 "standard" procedure) provided a pillared material in the case of
 vermiculite (I.sub.18 /I.sub.10 =6.0). For the mica, a very small fraction
 was pillared.
 Run 4.
 Experiments in which vermiculite was directly leached with citric acid
 followed (after washing the solid) by Na-exchange (step 4) and
 Al-pillaring (step 5), thus omitting steps 1 and 2 led to partial
 pillaring, in spite of the fact that the CEC of the Na-exchanged material
 obtained at step 4 was 1.49 meq g.sup.-1 (1.50 meq g.sup.-1 when treated
 with nitric acid). The I.sub.18 /I.sub.10 ratio was 1.2 (1.1 in a
 duplicate trial). This result indicates that freeing the exchange
 positions of the starting vermiculite and converting it to a homoionic
 form are not sufficient to ensure adequate pillaring (adequate pillaring
 meaning that a predominant fraction of the sample is pillared).
 Run 6.
 Carrying out steps 1, 4 and 5 following the standard conditions (steps 2
 and 3 omitted) resulted in the nearly total absence of pillaring. The
 I.sub.18 /I.sub.10 peak ratio was only 0.46. This confirms that step 2 is
 indispensable to the obtention of a well-pillared vermiculite.
 Trials Related to Step 3 (Complexing Agent)
 Run 7.
 Pillared vermiculite with acceptable characteristics (spacing, surface area
 and micropore volume) could be obtained when the citric acid treatment was
 suppressed. However, carrying out this treatment resulted in a significant
 improvement of the characteristics of the pillared material. Using oxalic
 acid had a similar beneficial effect, whereas no improvement was noticed
 when using nitric acid instead of citric or oxalic acid in step 3. Other
 complexing agents (f.i. acetylacetone) were less efficient or needed
 longer contact times than complexing acids.
 Trials Related to Step 4 (Na-exchange)
 Run 8.
 Attempts to suppress step 4 (sodium exchange) or to pillar
 ammonium-exchanged vermiculite were unsuccessful; no pillaring at all was
 observed. However, using calcium instead of sodium provided well pillared
 materials with slightly higher micropore volumes and improved resistance
 of the specific surface area to thermal treatment (compare P5-600 (Na)
 rand P5-600 (Ca) of Table 11). Exchange with hydrated cations is thus of
 crucial importance to the obtention of well pillared vermiculites (as well
 as for micas) and, in particular, the degree of completion of the
 exchange. Indeed, a clear relation exists between the degree of exchange
 and the fraction of pillared vermiculite.
 Application Areas of Pillared Micas and Vermiculites
 Pillared micas and vermiculites may be used as catalysts, as such and/or in
 adjunction with other catalytic components, for the following reactions:
 cracking-hydrocracking, isomerisation-hydroisomerisation, dewaxing,
 alkylation and dealkylation, disproportionation-transalkylation, upgrading
 of light cycle oils, oligomerisation of olefins, dehydration of alcohols,
 hydration of olefins, ether formation, hydroxylation of phenols and
 derivatives, condensation reactions, methanol to hydrocarbons,
 bydroformylation, synthesis of glycols, CO hydrogenation, Fischer-Tropsch,
 synthesis gas, HDS, HDN, HDM, NO reduction, deep oxidation,
 photocatalysis.
 Pillared micas and vermiculites may find application as adsorbents; in gas
 separation, as scavenger for heavy metals (treatment of waste waters);
 SO.sub.2, NO.sub.X abatement; in cation-selective composite membranes, as
 solid electrolytes; host material for (conducting) polymers; as host
 material for dispersed nitrides, oxynitrides, carbides, perovskites;
 modified electrodes.
 In particular, the pillared micas and vermiculites obtained according to
 the present invention may be used in any combination with other catalytic
 systems as, f.i. zeolites, oxides and mixed oxides. They may also be used
 as a support to metals, metal oxides and metal compounds.
 Chemical treatment(s) aiming to modify the surface properties of the
 pillared micas and vermiculites, such as treating with, e.g. phosphorus-
 and sulphur-containing compounds, are within the scope of this invention.
 Catalytic Examples
 Hydroconversion of Paraffins
 Hydroisomerization of octane was conducted in the vapour phase on
 Pt-impregnated samples (1 wt % Pt) of Al-pillared vermiculites and micas
 and on a commercial zeolite Beta (ZB25 from P.Q. Zeolites) as a reference.
 Impregnation and activation were similar to those reported in [reference
 19].
 Total flow of octane-/hydrogen mixture was 10 ml min-1, WHSV: 0.92 h-1,
 H2/C8:15.6. Reaction was made in temperature-programmed mode (0.2.degree.
 C. min-1) between 150 and 400.degree. C. On-line analysis of the reaction
 products was done in a gaschromatograph equipped with flame ionisation
 detector and CPSil-5 capillary column. The results obtained over the
 zeolite beta (ZB25) and different samples of pillared micas (symbolized by
 F) and vermiculites (S) are shown in FIGS. 7 and 8, where the variation of
 total conversion, of the yields of isomers and of the cracked products are
 plotted against reaction temperature. Higher yields of C8 isomers are
 produced over the pillared micas and vermiculites compared with the
 reference catalyst, with, at maximum isomerisation conversion, yields of
 80% for the pillared micas and vermiculites compared with 70% for the
 H-Beta zeolite, and selectivities to C8 isomers between 89.6 and 92.4% vs
 86.2 for the zeolite.
 For sake of comparison, results obtained at maximum isomerisation onversion
 on US-Y zeolites (commercial samples CBV400 to CBV780, from PQ Zeolite),
 H-Beta (ZB25 and ZB75 from PQ Zeolite), Al-pillared saponite (Al(ACH)PSY,
 a pilor scale prepared sample with Al-chlorhydrol), and on Al-pillared
 micas (samples F) and Al-pillared vermiculites (samples S), all loaded
 with 1 w t% Pt and tested in similar conditions are compiled in Table 17.
 Sample 3S044 in this table is an Al-pillared vermiculite that was treated
 with diluted hydrochloric acid after being calcined at 500.degree. C.
 (referred to as stabilized pillared vermiculite), together with those
 obtained on ZB25 (H-beta zeolite), Al pillared saponite (Al(ACH)PSY) and
 non stabilized Al-pillared vermiculite (1S044). The corresponding curves
 are shown in FIG. 9. Higher performances (conversion, yield of isomers and
 selectivities) were obtained for the pillared materials of the invention.
 In particular, the activity of the stabilized sample was significantly
 improved compared with non stabilized counterparts.
 TABLE 17
 Results obtained at maximum isomerization conversion over some zeolites,
 an Al-pillared saponite (AlP-S), and over Al-pillared micas (samples F) and
 Al-pillared
 vermiculites (samples S).
 Catalyst T max Total Yiso Sel.
 Si/Al iso conv i-C8 Ycr i-C8 Mono-iso Di-iso 2MC7/
 1% Pt (.degree. C.) (%) (%) (%) (%) (%) (%) /3M
 C7
 CBV 2.6 246 76.5 62.7 13.9 81.9 69.6 30.4 0.86
 CBV 2.6 182 68.3 51.8 16.5 75.8 68.4 31.6 0.91
 CVB 2.8 215 80.5 63.7 16.6 79.1 65.5 34.5 0.83
 CVB 13.0 220 83.4 66.9 16.6 80.2 62.2 37.8 0.84
 CVB 21.0 267 79.8 67.2 12.7 84.1 66.2 33.8 0.82
 CVB 30.0 270 76.7 61.5 16.2 78.9 72.2 27.8 0.82
 CVB 37.1 269 80.2 67.1 13.1 83.7 68.1 31.9 0.81
 ZB-75 37.5 212 79.2 68.3 10.9 86.3 68.2 31.8 0.89
 ZB-25 13.2 194 84.7 71.0 13.7 83.8 61.5 38.5 0.88
 AlP-S 244 83.7 67.8 16.0 81.0 66.2 33.8 0.85
 1F029 242 87.9 78.7 9.2 89.6 62.3 37.7 0.85
 6F010 238 85.6 79.1 6.5 92.4 64.1 36.0 0.86
 1F041 241 86.4 79.1 7.4 91.5 63.8 36.2 0.85
 2F045 238 88.0 80.0 7.9 91.0 65.8 34.2 0.85
 2F047 246 83.6 76.8 6.9 91.8 65.8 34.2 0.85
 1S044 241 87.8 78.9 8.9 89.9 62.3 37.7 0.85
 3S037 222 86.9 80.2 6.7 92.3 62.4 37.6 0.88
 3S044* 207 89.5 83.3 6.2 93.1 59.7 40.3 0.90
 *stabilized
 A duration test was performed over a stabilized Pt-impregnated (0.5 wt %
 Pt) Al-pillared mica at 207.degree. C. and WHSV of 0.92 h.sup.-1. After
 190 h time on stream, no deactivation was noticed, with a total average
 conversion of 88.2% and yield of C8 isomers of 82.8% (selectivity of
 93.9%).
 Reduction of NO by NH.sub.3
 A sample of pillared mica and a commercial zeolite ZSM-5 (SM-27,
 Si/Al=12-13.5, from VAW Aluminium AG) were twice Cu-exchanged with 2 M
 solution of copper nitrate at 80.degree. C. for 1 h, and removal of excess
 salt. The catalytic tests were carried out in a fixed-bed microreactor on
 50 mg samples diluted in small-sized quartz. The catalysts were heated at
 90.degree. C. for 2 h in flowing dry air. The reaction conditions were as
 follows: total flow: 200 ml min.sup.-1 (40 ml min.sup.-1 of NO, 5.000 ppm
 in He; 56 ml min.sup.-1 NH.sub.3, 5.000 ppm in He; and air=104 ml
 min.sup.-1 (10.5% O.sub.2 vol/vol). WHSV was 0.18 g NO g cata.sup.-1
 h.sup.-1. On-line gas phase analysis was done in a Rotork
 Chemiluminescence NOx Analyzer. The experimental values were taken at
 stabilized conversions. The comparative results are shown in FIG. 10. Both
 Cu-ZSM-5 and Cu--Al-pillared mica (M5) exhibited similar performances,
 total reduction of NO being attained at about 200.degree. C. in the
 zeolite and at above 300.degree. C. for the Cu-exchanged Al-pillared mica.
 REFERENCES
 1. Rich, C. I., Soil Sci. Soc. Am. Proc. 24,26, 1960.
 2. Hsu, P. H. and Bates, T. F., Soil Sci. Soc. Am. Proc. 28, 763, 1964.
 3. Brydon, J. E. and Tumer, R. C., Clays Clay Miner. 20, 1, 1977.
 4. Barnishel, R. I., in Minerals in Soil Environments, Soil Sci. Soc.
 Amer., Madison, p.331, 1977.
 5. Schutz, A. and Poncelet, G., unpublished results
 6. Hsu, P. H., Clays Clay Miner. 40, 300, 1992.
 7. d'Espinose de la Caillerie, J. B. and Fripiat, J. J., Clay Miner. 29,
 133, 1994.
 8. Michot, L. J. et al., Clay Miner. 29, 133, 1994.
 9. Vaughan, D. E. W., and Lussier, R. J., Proc. 5th Zeolite Conf., L. V.
 Rees (Ed.), Heyden & Sons, 94, 1980.
 10. Akitt, J. W. et al., J. Chem. Soc., Dalton Trans. 604, 1972
 11. Bottero, J. Y. et al., J. Phys. Chem. 84, 2933, 1980
 12. Lahav, N. et al., Clays Clay Miner. 26, 107, 1978.
 13. Schutz, A. et al., J., Clays Clay Miner. 35, 251, 1987.
 14. Zhonghua, G. et al., Microporous Mater., 3, 165, 1994.
 15. Bergaoui, L. et al., Chem. Soc. Faraday Trans. 91, 2229, 1995.
 16. de Boer, J. H. and Broekhoff, J. C. P., J. Catal. 10, 391, 1968.
 17. Remy, M. J. et al., Microporous Mater. 7(6), 287, 1996.
 18. Sing, K. S. W. et al., Pure Appl. Chem. 57, 603, 1985.
 19. Moreno, S. et al., J. Cattil. 162, 198, 1996.