Bergaya F. Handbook of Clay Science

Подождите немного. Документ загружается.

of the exchangeable cation (van Olphen, 1970). The explanation seems to lie in the

surface heterogeneity of phyllosilicates. These minerals have at least two types of

surfaces, basal, and edge, with different chemistry and properties. In kaolinite, the

reactive surfa ces are mainly located on particle edges (Cases et al., 1986, 2000). The

effect of surface heterogeneity on gas adsorption should be assessed from adsorp tion

in the very low-pressure region, during the formation of the ﬁrst monolayer on the

surface. This kind of information may be obtained from quasi-equilibrium set-ups

equipped with accurate pressure sensors (Michot et al., 1990; Villie

ras et al., 1992,

1997b, 2002a). The experimental data are plotted as the derivative of the amount

adsorbed versus the logarithm of the relative pressure as shown in Fig. 12.9.2.

The importance of the derivative plot is that the abscissa is proportional to the

free energy of adsorption. Thus, the derivative curve can be considered as a ﬁn-

gerprint of the adsorption energy distribution of the gas probe. Such a curve can be

further analysed on a quantitative basis using the ‘derivative isotherm summation’

(DIS) method developed by Villie

ras et al. (1992, 1997a, 1997b).

Argon can be used to obtain information on the shape of clay mineral particles.

The derivative curves are always similar in shape to that shown in Fig. 12.9.2 for talc

(layer charge ¼0). The DIS method allows the SSA of the basal (low-energy

adsorption) and edge/lateral (medium-energy adsorption) surface to be calculated

(Villie

ras et al., 1992, 1997a, 1997b, 2002a; Michot et al., 1994; Bardot, 1998; Cases

et al., 2000; Michot and Villie

ras, 2002). For clay minerals with a layer charge >0,

0.5

1.5

-16 -12 -8 -4 0

dVads / d ln(P/Po)

ln (P/Po)

Basal surfaces

Lateral surfaces

High energy

adsorption sites

Fig. 12.9.2. Example of derivative adsorption isotherm obtained in the case of talc/argon at

77 K. From Michot et al. (1994).

Chapter 12.9: Surface Area and Porosity968

such a procedure yields correct basal and lateral surface areas only with small

monovalent exchangeable cations, such as lithium and sodium since larger cations

interfere with the formation of an adsorbed ﬁlm (Bardot, 1998).

Low-pressure adsorption and derivative plots also give information on speciﬁc

adsorption sites. In the case of talc , additional high-energy adsorption sites are

observed with argon (Fig. 12.9.2). Quantitative DIS an alysis indicates that these sites

are identiﬁable with the ditrigonal holes in the tetrah edral sheet (Michot et al., 1994).

Such sites are also present in low-charge synthetic sapo nites (Michot and Villie

ras,

2002) and layered silicas (Eypert-Blaison et al., 2002) but not in high-charge sapo-

nites, kaolinites, or illites.

When nitrogen is used, speciﬁc interactions can take place between the probe

molecules and the polar surface sites (Villie

ras et al., 1997b, 2002a, 2002b). As a

consequence, the shape of the nitrogen derivative plots differs from that of argon,

and the plots are less easy to interpret. High-energy sites, identiﬁable with empty

ditrigonal holes, are present on basal surfaces of clay minerals whatever the layer

charge. Additional sites, corresponding to interaction between nitrogen and surface

cations were identiﬁed in synthetic saponites (Michot and Villie

ras, 2002) and pro-

bably exist in other charged minerals.

In conclusion, the accurate determination of the SSA of clay minerals is not

straightforward and nitrogen may not be the best probe to use for this purpose.

Nevertheless, the BET-N

SSA commonly serves as a reference as nitrogen is the

most widely used gas for the BET analysis (van Olphe n, 1970). As described below,

other techniques for measuring the SSA of clay minerals were proposed. A pro-

mising method is atomic force microscopy (AFM) (Bickmore et al., 2002)asitcan

provide important complementary information.

12.9.2. SWELLING CLAY MINERALS

The determination of the SSA of swe lling clay minerals is rather complicated since

the measured value depends on sample preparation, the adsorbate used, and the

nature of the exchangeable cation. In principle, the total speciﬁc surface area of

swelling clay minerals can be deduced from the unit cell parameters: a, b,andc.

Indeed, for isolated clay mineral layers considered as inﬁnite bi-dimensional plate-

lets, the surface area can be written as

2ab=ðd abcÞ¼2=cd

where d is the solid density.

Depending on the values for c and d, the surface area thus determined varies

between 700 and 850 m

/g. This is the maximum surface area available for the ad-

sorption of any compound. Since the SSA deduced from adsorption experiments

depends on whether or not the adsorbed species can induce swelling (and gain access

12.9.2. Swelling Clay Minerals 969

to the internal/interlayer surface), the SSA values for a given sample can be highly

variable (van Olphen, 1970). It is useful, therefore, to make a distinction between

adsorbates that induce swelling and those that do not.

A. Adsorbates that Induce Swelling

For swelling (expanding) clay minerals, the adsorbates that can induce swelling are

polar molecules such as water, alcohols, etc. Thus the ﬁrst problem of surface area

determination is to deﬁne the initial state that is reached after outgassing the sample,

prior to its analysis. Similar outgassing conditions (e.g., 110 1C and a residual vac-

uum of 0.1 Pa) can result in different initial states due to variable water contents.

This is well illustrated by CRTA (Rouquerol, 1970, 1989; Rouqu erol et al., 1992)

measurements on Wyoming montmorillonite exchanged with different cations

(Table 12.9.1)(Berend et al., 1995; Cases et al., 1997).

At a given outgassing temperature, the residual water content strongly depends on

the nature of the cation. In terms of water molecules per cation, the number varies

between 1.0 for K

and 4.4 for Ca

. As a result, the number of sites available for

adsorption will be variable. Furthermore, when adsorbates can access the interlayer

space and induce swelling, the situation is rather complicated. This is because the

number of sites available for adsorption changes along the adsorption isotherm in a

way that strongly de pends on the nature of the interlayer cation. This feature can

clearly be observed when comparing the adsorption isotherms for water on Wyo-

ming montmorillonite exchanged with various interlayer cations (Fig. 12.9.3)

(Berend et al., 1995; Cases et al., 1997). It must also be noted that the reproducibility

of these isotherms for divalent-exchanged montmorillonites is not perfect because of

small differences in sample preparation and pretreatment conditions. In that case, a

direct application of the BET treatment in the classical range of relative pressure

0.05–0.25 would lead to the values listed in Table 12.9.2.

The monolayer volume thus determined strongly depends on the nature of the

interlayer cation. Indeed, the BET equation cannot be applied to montmorillonites

exchanged with rubidium and cesium ions because there is no relative pressure region

where the BET transform (Eq. (1)) displays a linear behaviour. Even if the problems

associated with the choice of the cross-sectional area for water molecules (van

Olphen, 1970) are disregarded, no true SSA value can be derived. Such isotherms can

Table 12.9.1. Number of water molecules coordinated to the exchangeable cations after out-

gassing different homoionic Wyoming montmorillonites at 110 1C under a residual pressure of

0.1 Pa

Exchangeable cation Li

Water molecules per exchangeable cation 1.54 1.36 1.0 1.18 1.02 4.2 4.4 3.2 1.8

Chapter 12.9: Surface Area and Porosity970

0 0.2 0.4 0.6 0.8 1

P/P

0 0.2 0.4 0.6 0.8 1

P/P

0 0.2 0.4 0.6 0.8 1

P/P

0 0.2 0.4 0.6 0.8 1

P/P

0 0.2 0.4 0.6 0.8 1

P/P

0 0.2 0.4 0.6 0.8 1

P/P

0 0.2 0.4 0.6 0.8 1

P/P

0 0.2 0.4 0.6 0.8 1

P/P

0 0.2 0.4 0.6 0.8 1

P/P

K Rb Cs

Mg Ca

Sr Ba

Adsorbed amount (mmoles/g)

Fig. 12.9.3. Water adsorption–desorption isotherms obtained at 303 K for different homoionic Wyoming montmorillonites.

12.9.2. Swelling Clay Minerals 971

only be interpreted in terms of the evolution of interlayer distances with water

relative pressure together with spectroscopic information about the status of

adsorbed water molecules.

Fig. 12.9.4 shows the changes of interlayer spacing with water relative pressure for

the same sample as that described in Fig. 12.9.3. The curves are similar in shape to

the adsorption isotherms and provide some insights into water adsorption mech-

anisms. For samples exchanged with divalent cations and lithium, water molecules

can enter the interlayer space at the lowest relative pressures investigated. However,

this is not the case for the other monovalent cation-exchanged montmorillonites. On

the basis of these data and using different assumptions about the energetics of the

clay mineral surface, it is possible to derive adsorption isotherms for water on the

external and inter nal surfaces of swelling clay minerals. This improves understanding

of adsorption mechanisms.

In the case of other swelling-inducing adsorbates such as methanol and is-

opropanol (Annabi-Bergaya et al., 1 979, 1980a, 1980b, 1981), the nature of the

interlayer cation also has a strong inﬂuence on adsorption features. Here, too, it is

not possible to derive surface areas from such experiments. A detailed knowledge of

the structural evolution of the particles along the adsorption isotherm is required to

unravel the complex behaviour of swelling clay minerals. Spectrosco pic information

on the status of adsorbate molecules may also be needed.

Other swelling-induc ing adsorbates such as ethylene glycol monoethyl ether

(EGME), methylene blue (MB), and para-nitrophenol (pNP) were used for deter-

mining the SSA of clay minerals and soils (Theng, 1995; Helmy et al., 1999; Kozak i

et al., 1999; Hedley et al., 2000, Parﬁtt et al., 2001). For non-swelling clay minerals

and metal (hydr)oxides, the SSA values derived from adsorption of pNP are within

10% of the corresponding BET-N

areas (Theng, 1995). Since EGME, MB, and pNP

can penetrate the interlayer space of swelling clay minerals, the SSA values derived

Table 12.9.2. Monolayer volumes and C constants determined by application of the BET

equation at relative pressures 0.05–0.25 for different homoionic Wyoming montmorillonites

Interlayer cation C constant Monolayer volume (cm

1

)

30 76.1

6.3 28.7

5.1 25.0

n.d. n.d.

25 136.6

9.2 120.3

11 80.4

12.5 80.4

n.d. ¼ not determined.

Chapter 12.9: Surface Area and Porosity972

from their adsorption are assumed to include the internal surface area of the mineral,

that is, the total accessible surface area.

However, experimental conditions, layer charge, and the nature of the exchange-

able cations significantly affect the results. For instance, Kahr and Madsen (1995)

show that reliable surface areas can only be obtained by adsorption of MB when the

layer charge is compatible with the size of adsorbed MB. This corresponds to a layer

charge between 0.28 and 0.33 per half unit cell.

In the case of EGME, both the nature of the exchangeable cation and the mag-

nitude of layer charge modify the apparent cross-sectional area of the adsorbed

0 0.2 0.4 0.6 0.8 1

d-spacing (Å)

P/P

0 0.2 0.4 0.6 0.8 1

P/P

0 0.2 0.4 0.6 0.8 1

P/P

Na K

0 0.2 0.4 0.6 0.8 1

P/P

0 0.2 0.4 0.6 0.8 1

P/P

d-spacing (

)

0 0.2 0.4 0.6 0.8 1

P/P

0 0.2 0.4 0.6 0.8 1

P/P

0 0.2 0.4 0.6 0.8 1

P/P

0 0.2 0.4 0.6 0.8 1

P/P

Mg Ca Sr Ba

Fig. 12.9.4. Basal spacing of homoionic Wyoming montmorillonites as a function of the

relative pressure of water.

12.9.2. Swelling Clay Minerals 973

molecule (Kelloma

ki et al., 1987, 1989; Chiou and Rutherford, 1993, 1997). This

leads to the conclusion that reliable surface areas cannot be measured using this

method. Nevertheless the EGME retention method can provide useful comparative

data for soils and soil clays (Tiller and Smith, 1990; Churchman et al., 1991).

Moreover, recent measurements show that the SSA derived from EGME retention is

correlated with the cation exchange capacity (Abdullah et al., 1999; Bigorre et al.,

2000), renderi ng the use of this technique even more dubious.

B. Adsorbates that do not Induce Swelling

When the adsorbate does not induce swelling, the nitrogen or argon adsorption

isotherm characterises the dry state, and can provide some information about the

size, structure, the different porosities (Chapter 1) and sometimes shape of clay

mineral particles and aggregates. The analysis of the hierarchical porosity (see

Chapter 1) of swelling clay minerals is somewhat problematic. Indeed, the organ-

ization of the particles and aggregates strongly depends on preparation conditions

that, in turn, can inﬂuence the determination of surface areas, micropore volumes,

and mesopore size distributions.

For instance, the N

SSA of a freeze-dried powder of Wyoming Na

-montmo-

rillonite is close to 45 m

/g whereas a ﬁlm of the same sample has a surface area of

about 35 m

/g (Bihannic, 1998). In terms of clay mineral characteristics, the nature of

the exchangeable cation strongly modiﬁes the SSA and pore volumes of dried sam-

ples as illustrated by measurements on cation exchan ged Wyoming montmorillonites

(Berend et al, 1995; Cases et al., 1997; Rutherford et al., 1997) and Arizona mont-

morillonites (Rutherford et al., 1997). For Wyoming montmorillonites, the measured

surface areas range from 30 m

/g for the calcium-to 130 m

/g for the cesium-

exchanged form. The microporosity of the Cs

-montmorillonite, deduced from the

t-plot, is also much higher than for the other cation-exchanged samples. This ﬁnding

may be ascribed to the large ionic radius of the Cs

ion (also indicated by the basal

spacing of 1.12 nm for dry samples), allowing access of some nitrogen molecules to

the interlayer space (Aylmore et al., 1970; Berend et al., 1995; Rutherford et al.,

1997). Such an explanation can only be proposed for bulky interlayer cations. In all

other cases, the investigated samples almost always have some micropores. Their

presence is due to (i) the turbostratic arrangement of clay mineral layers giving rise to

slit-shaped micropores at particle edges, the extent of which is strongly dependent on

both the crystal-chemistry of the clay mineral (size of elementary layers, charge,

nature of the cation) and preparation conditions; and (ii) the presence of high-energy

adsorption sites on the basal (planar) surfaces that are considered as micropores

when using classical procedures such as t-plots or a

plots.

The adsorption isotherms of gases that do not induce swelling indicate the pres-

ence of mesopores between particles. Some of these pores, especially the lenticular

type (Touret et al., 1990; Bihannic, 1998) are not accessible to such gases. The

amount adsorbed strongly dep ends on the nature of the exchangeable cation and

Chapter 12.9: Surface Area and Porosity974

sample preparation. Accessible pores generally exhibit a wide-size distribution that is

not easy to characterise by classical gas adsorption techniques. Likewise, the pore-

size distribution is strongly inﬂuenced by the nature of the exchangeable cation and

preparation conditions. Because of problems associated with the connectivity of the

pore network, the pore size distributions measured by gas adsorption and mercury

porosimetry are often affected by artefacts. Thus, these measurements reﬂect the

accessible porosity rather than the true poro sity (Sauze

at et al., 2001).

REFERENCES

Abdullah, W.S., Alshibli, K.A., Al-Zou’bi, M.S., 1999. Inﬂuence of pore water chemistry on

the swelling behavior of compacted clays. Applied Clay Science 15, 447–462.

Annabi-Bergaya, F., Cruz, M.I., Gatineau, L., Fripiat, J.J., 1979. Adsorption of alcohols by

smectites: I. Distinction between internal and external surfaces. Clay Minerals 14, 249–258.

Annabi-Bergaya, F., Cruz, M.I., Gatineau, L., Fripiat, J.J., 1980a. Adsorption of alcohols by

smectites: II. Role of the exchangeable cations. Clay Minerals 15, 219–223.

Annabi-Bergaya, F., Cruz, M.I., Gatineau, L., Fripiat, J.J., 1980b. Adsorption of alcohols by

smectites: III. Nature of the bonds. Clay Minerals 15, 225–237.

Annabi-Bergaya, F., Cruz, M.I., Gatineau, L., Fripiat, J.J., 1981. Adsorption of alcohols by

smectites: IV. Models. Clay Minerals 16, 115–122.

Aylmore, L.A.G., Sills, I.D., Quirk, J.P., 1970. Surface area of homoionic illite and mont-

morillonite clay minerals as measured by the sorption of nitrogen and carbon dioxide.

Clays and Clay Minerals 18, 91–96.

Bardot, F., 1998. Les Mine

raux Argileux et leur He

roge

ite

Superﬁcielle: Inﬂuence de la

Nature des Cations Compensateurs Superﬁciels de l’Illite sur les Me

canismes d’Adsorption

de Gaz. Ph.D. thesis. INPL Nancy.

Barrett, E.P., Joyner, L.G., Halenda, P.H., 1951. Determination of pore volumes and area

distributions in porous substances. I. Computation from nitrogen isotherms. Journal of the

American Chemical Society 73, 373–380.

Berend, I., Cases, J.M., Franc- ois, M., Uriot, J-P., Michot, L.J., Masion, A., Thomas, F., 1995.

Mechanism of adsorption of water vapor by homoionic montmorillonite. 2. The Li

,Na

,Rb

and Cs

exchanged forms. Clays and Clay Minerals 43, 324–336.

Bergaoui, L., Lambert, J.F., Vicente-Rodriguez, M.A., Michot, L.J., Villie

ras, F., 1995. Po-

rosity of synthetic saponites with variable layer charge pillared by Al

polycations.

Langmuir 11, 2849–2852.

Bickmore, B.R., Nagy, K.L., Sandlin, P.E., Crater, T.S., 2002. Quantifying surface areas of

clays by atomic force microscopy. American Mineralogist 87, 780–783.

Bigorre, F., Tessier, D., Pedro, G., 2000. Contribution des argiles et des matie

res organiques a

la re

tention de l’eau dans les sols. Signiﬁcation et roˆ le fondamental de la capacite

d’e

change

en cations. Comptes Rendus de l’Acade

mie des Sciences, Paris, Sciences de la Terre et des

Plane

tes 330, 245–250.

Bihannic, I., 1998. Structure et Microtexture du Gonﬂement Cristallin de la Montmorillonite.

The

se. Universite

d’Orle

ans.

Brunauer, S., Emmett, P.H., Teller, E., 1938. Adsorption of gases in multimolecular layers.

Journal of the American Chemical Society 60, 309–319.

References 975

Cases, J.M., Berend, I., Franc- ois, M., Uriot, J-P., Michot, L.J., Thomas, F., 1997. Mechanism

of adsorption of water vapor by homoionic montmorillonite. 3. The Mg

,Ca

,Sr

and Ba

exchanged forms. Clays and Clay Minerals 45, 8–22.

Cases, J.M., Cunin, P., Grillet, Y., Poinsignon, C., Yvon, J., 1986. Method of analysing

morphology of kaolinites: relations between crystallographic and morphological proper-

ties. Clay Minerals 21, 55–68.

Cases, J.M., Grillet, Y., Franc- ois, M., Michot, L., Villie

ras, F., Yvon, J., 1991. Evolution of

porous structure and surface area of palygorskite under vacuum thermal treatment. Clays

and Clay Minerals 39, 191–201.

Cases, J.M., Villie

ras, F., Michot, L.J., 2000. Le Point Sur: Les phe

nome

nes d’adsorption,

d’e

change ou de re

tention a

l’interface solide-solution aqueuse: 1 Connaissance des pro-

prie

s structurales, texturales et superﬁcielles des solides. Comptes Rendus de l’Acade

mie

des Sciences, Paris, Sciences de la Terre et des Plane

tes 331, 1–11.

Chiou, C.T., Rutherford, D.W., 1993. Sorption of N

and EGME on some soils, clays and

mineral oxides and determination of sample surface area by use of sorption data. Envi-

ronmental Science and Technology 27, 1587–1594.

Chiou, C.T., Rutherford, D.W., 1997. Effects of exchanged cation and layer charge on the

sorption of water and EGME vapors on montmorillonite clays. Clays and Clay Minerals

45, 867–880.

Churchman, G.J., Burke, C.M., Parﬁtt, R.L., 1991. Comparison of various methods

for the determination of speciﬁc surfaces of subsoils. Journal of Soil Science 42,

449–461.

de Boer, J.H., Lippens, B.C., Linsen, B.G., Broekhollf, J.C.P., van der Heuvel, A., Osinga,

Th.J., 1966. The t-curve of multiplayer N

-adsorption. Journal of Colloid and Interface

Science 21, 405–414.

Eypert-Blaison, C., Villie

ras, F., Michot, L.J., Pelletier, M., Humbert, B., Ghanbaja, J., Yvon,

J., 2002. Surface heterogeneity of kanemite, magadiite and kenyaite: a high resolution gas

adsorption study. Clay Minerals 37, 531–542.

Gregg, S.J., Sing, K.S.W., 1982. Adsorption, Surface Area and Porosity, 2nd edition.

Academic Press, London.

Grillet, Y., Cases, J.M., Franc- ois, M., Rouquerol, J., Poirier, J.E., 1988. Modiﬁcation of the

porous structure and surface area of sepiolite under vacuum thermal treatment. Clays and

Clay Minerals 36, 233–242.

Hedley, C.B., Saggar, S., Theng, B.K.G., Whitton, J.S., 2000. Surface area of soils of con-

trasting mineralogies using para-nitrophenol adsorption and its relation to air-dry moisture

content of soils. Australian Journal of Soil Research 38, 155–167.

Helmy, A.K., Ferreiro, E.A., Bussetti, S.G., 1999. Surface area evaluation of montmorillonite.

Journal of Colloid and Interface Science 210, 167–171.

Kahr, G., Madsen, F.T., 1995. Determination of the cataion exchange capacity and the sur-

face area of bentonite, illite and kaolinite by methylene blue adsorption. Applied Clay

Science 9, 327–336.

Kelloma

ki, A., Kuula-Va

isa

nen, P., Nieminen, P., 1989. Sorption and retention of ethylene

glycol monoethyl ether (EGME) on silicas. Journal of Colloid and Interface Science 129,

373–378.

Kelloma

ki, A., Nieminen, P., Ritama

ki, L., 1987. Sorption of ethylene glycol monoethyl ether

(EGME) on homoionic montmorillonites. Clay Minerals 22, 297–303.

Chapter 12.9: Surface Area and Porosity976

Kozaki, T., Sato, Y., Nakajima, M., Kato, H., Sato, S., Ohashi, H., 1999. Effect of particle

size on the diffusion behavior of some radionuclides in compacted bentonite. Journal of

Nuclear Materials 270, 265–272.

Michot, L., Franc-ois, M., Cases, J.M., 1990. Surface heterogeneity studied by quasi-equili-

brium gas adsorption procedure. Langmuir 6, 677–681.

Michot, L.J., Villie

ras, F., 2002. Assessment of surface energetic heterogeneity of synthetic

Na-saponites. The role of layer charge. Clay Minerals 37, 39–57.

Michot, L.J., Villie

ras, F., Franc-ois, M., Yvon, J., Le Dred, R., Cases, J.M., 1994. The

structural microscopic hydrophobicity of talc. Langmuir 10, 3765–3773.

Michot, L.J., Villie

ras, F., Lambert, J.F., Bergaoui, L., Grillet, Y., Robert, J.L., 1998. Surface

heterogeneity in micropores of pillared clays: the limits of classical pore-ﬁlling mechanisms.

Journal of Physical Chemistry B 102, 3466–3476.

Parﬁtt, R.L., Whitton, J.S., Theng, B.K.G., 2001. Surface reactivity of A horizons towards

polar compounds estimated from water adsorption and water content. Australian Journal

of Soil Research 39, 1105–1110.

Rouquerol, J., 1970. L’analyse thermique a

vitesse de de

composition constante. Journal of

Thermal Analysis 2, 123–140.

Rouquerol, J., 1989. Controlled transformation rate thermal analysis: the hidden face of

thermal analysis. Thermochimica Acta 144, 209–224.

Rouquerol, J., Borde

re, S., Rouquerol, F., 1992. Controlled rate evolved gas analysis: recent

experimental set-up and typical results. Thermochimica Acta 203, 193–202.

Rutherford, D.W., Chiou, C.T., Eberl, D.D., 1997. Effects of exchanged cation on the mi-

croporosity of montmorillonite. Clays and Clay Minerals 45, 534–543.

Sauze

at, E., Guillaume, D., Villie

ras, F., Dubessy, J., Franc- ois, M., Pfeiffert, C., Pelletier,

M., Ruck, R., Barre

s, O., Yvon, J., Cathelineau, M., 2001. Caracte

risation min-

ralogique, cristallochimique et texturale de l’argile MX-80. Rapport ANDRA n1 CRP

0ENG 01-001.

Sing, K.S.W., Everett, D.H., Haul, R.A.W., Moscou, L., Pierotti, R.A., Rouquerol, J.,

Siemieniewska, T., 1985. Reporting physisorption data for gas/solid systems with special

reference to the determination of surface area and porosity. Pure and Applied Chemistry

57, 603–619.

Theng, B.K.G., 1995. On measuring the speciﬁc surface area of clays and soils by adsorption

of para-nitrophenol: use and limitations. In: Churchman, G.J., Fitzpatrick, R.W.,

Eggleton, R.A. (Eds.), Clays: Controlling the Environment. Proceedings of the 10th In-

ternational Clay Conference, Adelaide, Australia, 1993. CSIRO Publishing, Melbourne,

pp. 304–310.

Tiller, K.G., Smith, L.H., 1990. Limitations of EGME retention to estimate the surface area of

soils. Australian Journal of Soil Research 28, 1–26.

Touret, O., Pons, C.H., Tessier, D., Tardy, Y., 1990. Etude de la re

partition de l’eau dans des

argiles sature

es Mg

aux fortes teneurs en eau. Clay Minerals 25, 217–233.

van Olphen, H., 1970. Determination of surface areas of clays—evaluation of methods. In:

IUPAC Supplement to Pure and Applied Chemistry, Surface Area Determination, But-

terworths, London, 255–271.

Villie

ras, F., Cases, J.M., Franc- ois, M., Michot, L., Thomas, F., 1992. Texture and surface

energetic heterogeneity of solids from modelling of low pressure gas adsorption isotherms.

Langmuir 8, 1789–1795.

References 977