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Thermal dehydration of mono- and di-valent montmorillonite cationic derivatives
211
Thermochimica Acta, 85 (1985) 211-214 Elsevier Science Publishers B.V., Amsterdam -Printed
THERMAL
DEHYDRATION
OF MONO- AND DI-VALENT
in The Netherlands
MONTMORILLONITE
CATIONIC
DERIVATIVES
Nabila M. GUINDY, Department
T.M. EL-AKKAD,
of Chemistry,
Ain Shams University,
N.S. FLEX,
Faculty
Abbassia,
S.R. EL-MASSRY,
and S. NASHED
of Science, Cairo, Egypt.
ABSTRACT The kinetics of the isothermal dehydration of seven derivatives of JelsovyPotok montmorillonite constituting two series of mono- and di-valent cations were studied together with TG and DTA. A certain correlation was established between the charge density and (1) the highest dehydration DTA peak (2) the first order rate constant for the dehydration reaction. The results support a diffusion controlled mechanism for th:ldehydration with an energy and entropy of activations23 kJ mol-1 and -220 JK , respectively. INTRODUCTION In view of the wide application the effects
of thermal
dehydroxylation
treatment
and structure
Birch Holt et al investigated Mikhail pheres
et al studied
of clay minerals
on its properties
changes
became
of interest
the rate of thermal
the dehydration
in industry
especially
the study of
its dehydration,
in the past decade.
dehydration
of some clay minerals
of muscovite in various
(1).
atmos-
(2-4).
The present
study deals with the effect of exchangeable
DTA and the kinetics
of isothermal
dehydration
cations
of Jelsovy-Potok
on the TG,
montmorillonite.
EXPERIMENTAL The Jolsovy-Potok of different
exchangeable
Ca-Mg montmorillonite) cations, hours.
namely,
cations
derivatives
were prepared
by soaking 5g. of the original
in 100~~. of 0.1 N chloride
Li'+, Na', Cs+, Mg2+,
The prepared
solution
montmorillonite
derivative
and then with alcohol
and were kept under a relative
Ca2+,
was washed
sample
(usually
solution of the various
Sr2+ and Ba2' for a period of 12 five times with the specific
until the solution humidity
by replacement
chloride
was free from chloride
of 51.5-55%
in the temperature
ions
range
18-2O'C. Differential according
thermal
to the technique
Thermogravimetric an automatic
was carried out in a locally made apparatus
adopted by Mackenzie
analysis
thermobalance
0040-6031/85/$03.30
analysis
and kinetic
provided
(5) and McAdie
experiments
by Gebruder
0 Elsevier Science Publishers B.V.
Netzsch,
were
(6).
carried
out using
West Germany.
212 RESULTS
AND DISCUSSION
Thermogravimetric
and Differential
TG and DTA indicate ca 15O'C before
Thermal
that dehydration
dehydroxylation
region
more or less similar
derivatives,
(50-150°C),
attributed
whereas
of all the derivatives
hydration
is related
bonding
energy holding
derivatives tendency cation
studied
them inbetween
peaks are
(7-9).
water molecules
origin
The variation
the clay flakes.
The tendency
in
in the de-
liberated
to display more than one peak above 100°C, is attributed
of hydrated
at
show that they differ mainly
their dehydroxylation
to the amount of water molecules
and the of some to the
to form more than one shell surrounding
the
(8).
The effect of the charge density peak as a measure surface
of the potential
of the cation
ship was obtained difference Kinetics
energy binding
and the presence
surface on the highest DTA
the inner water
a satisfactory
shell to the
linear relation-
of two linear plots is related
to the
in the cation character.
of the Isothermal
DTA and TG results,
Dehydration
indicate
that the suitable
dehydration
isotherms
obeyed
constant,
k, are given in Table 1.
Mikhail
of the cation
is shown in Fig. 1, where
study of the isothermal
is between
first order kinetics
50'
temperature
range for the
and 150°C.
The dehydration
and the values
of the first order rate
First order kinetics
were also reported
by
et al (Z-4).
Table
1 shows that the k values,
for the divalent multivalent dehydration increases increase
cations
are higher
of the same cationic
cations
to tie clay mineral
process
(10).
the distance
an increase
Mg in vermiculite
contaminating
of separation
the dehydration
flakes
betweeen
than those
due to the tendency
together
to the tendency
reaction.
in the c dimension
and thus hindering as the cationic of large cations
the layers of montmorillonite
of the radius to and
This was proved by Walker who re-
from 14.4 to 15 A0 when Sr was replaced
by
(10).
The Ba derivative to the possibility
for the monovalent
radius,
It also shows that k increases
for the same series attributed
thus facilitating ported
to completion
at ca SOO'C.
to the use of the same clay mineral
the preparation peaks
takes place almost
starts and achieved
DTA of the seven montmorillonite in the dehydration
Analysis
is the only exception
of low temperature
the derivative
during
at low temperatures,
dehydroxylation its preparation.
probably
of Ba(OH)* which
due
could be
213
?tKfzx+ last
IlTA'penk
Catianic radius
(OC)
Fig.2 Variation cationic radius.
Fig.1 Variation of the last DTA peak with the charge density.
(A')
of k with the
TABLE 1. Values of the cationic radius, charge density and the first order rate-constant, for the various montmorillonite derivatives.
7o"c
85'C
100°C
120°c
140°c
Cationic* charge density (Cm-*I
Li
0.32
0.38
0.53
0.89
1.27
0.60
3.540
Na
0.41
0.64
0.91
0.65
1.80
0.95
1.410
CS
0.56
1.15
1.32
1.94
2.66
1.69
0.446
Mg
0.23
0.47
-
0.60
0.86
0.65
6.036
0.42
0.85
1.03
1.38
0.99
2.600
Ca Sr
0.34
0.70
0.96
1.22
1.53
1.13
1.990
Ba
0.33
0.42
1.02
-
1.67
1.35
1.400
A plot of k (s-l) at 14O'C against line for each group of derivatives, about the same gradient They differ
the cationic
The variation the cation, Table the variation flakes which
suggesting
in the electrostatic their distance and/or
the water molecules
adjacent
and third layers which The previous which
charge density
gave a straight lines are of to be operative.
due to the inhibition
of the reaction
rate constant with the charge density
to either
or both of the following
attraction
forces between
of separation
the change
= cationic
covalent bonds between
of mobile water molecules.
by considering
by the rate of desorption
of water molecules
through
charge/4Tr2.
the clay mineral
surface and those of the second
the fluidity
are confirmed
on
factors,
and hence the flow of water
in the partially
to the clay mineral
conclusions
by the rate of diffusion
Cationic
one and the same mechanism
in turn affects
is governed
radius,
two straight
charge.
1, is attributed
affects
The
Fig. 2.
of the dehydration
during dehydration,
hydration
the cationic
in the value of the intercept
upon increasing
*
Cationic radi s x 10'lo (In)
k x 10' (s-l)
Cationic derivative
the mechanism
of de-
from the surface followed
the lattice
interface.
If
214 the desorption changeable or probably obtained.
is rate determining,
to visualize
how the ex-
could affect the dehydration
rate and a value of the order of
higher
than the heat of evaporation
of water
Thus the diffusion
ed earlier,
it is difficult
cations
the exchangeable
reaction
cations affect the interlayer
water molecules
diffuse
micelle
Such a process would
edge.
(Z-4) would have been
is the rate determining,
from the hexagonal
since as mention-
spaces through which
holes in the sheet surface
involve an absorption
into the
of energy to push the
layers apart (12). A relatively high value of the energy of activation, Ea,ca -1 23kJmol , was obtained for all the derivatives studied attributed to a phenomenon known as "activated al diffusion", sional flow
was reported
energy of activation actions right
diffusion"
increase
in the value of Ea.
to yield two to three times higher values
than that of the three dimensional
(13), and is expected angles to the flakes.
the entropy
(2-4) or to what is known as "two dimension-
both lead to an apparent
of activation
to be due to a restricted
This is supported -1 ca 220 JK .
Two dimenof the free
due to the lateral translational
by a large negative
inter-
motion value
at
for
REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.
J. Birch Holt, I.B. Culter and M.E. Wadsworth, J. Am. Ceram. Sot., 41, (1958), 842. R.Sh. Mikhail, N.M. Guindy, and S. Hanafi, J. Appl. Chem., 20, (1970), 346. R.Sh. Mikhail and N.M. Guindy, J. Appl. Chem. Biotechnol. 21, (1971), 113. R.Sh. Mikhail, N.M. Guindy and S. Hanafi, Thermochimica Acta, 29, (1978), 289. R.C. Mackenzie, Differential Thermal Investigation of Clays, Mineralogical Section, London, 1957, reprinted 1966. H.G. McAdie, Anal. Chem., 39 (1967), 543. C.F. Walker and W.C. Cole, in "The Differential Investigation of Clays", Edited by R.C. Mackenzie, Mineralogical Society, London, 1957, 191 pp. G.T. Faust, Am. Miner, 36, (1951), 795. C.A. Alexinals, and M.I. Jackson 14th Nat. Conf. Clays and Clay Minerals, Berkeley, C.A., Pergamon Press, London 1966, 35 pp. G.F. Walker, Proc. Intern. Clay Conf., Stockholm, 1963, 177 pp. P.F. Low, in Clay Mineralogy, Edited by Grim, R.E. McGraw-Hill, 1968, 256 pp. R.C. Mackenzie and B.M. Bishui, Clay Minerals Bulletin, 3, (1957), 276. and Eyring in "The Theory of Rate Processes", Edited by S. W.J. Moore Glasstone, K.J. Laidler and H. Eyring, McGraw-Hill 1941, 512 pp.
Thermochimica Acta, 85 (1985) 211-214 Elsevier Science Publishers B.V., Amsterdam -Printed
THERMAL
DEHYDRATION
OF MONO- AND DI-VALENT
in The Netherlands
MONTMORILLONITE
CATIONIC
DERIVATIVES
Nabila M. GUINDY, Department
T.M. EL-AKKAD,
of Chemistry,
Ain Shams University,
N.S. FLEX,
Faculty
Abbassia,
S.R. EL-MASSRY,
and S. NASHED
of Science, Cairo, Egypt.
ABSTRACT The kinetics of the isothermal dehydration of seven derivatives of JelsovyPotok montmorillonite constituting two series of mono- and di-valent cations were studied together with TG and DTA. A certain correlation was established between the charge density and (1) the highest dehydration DTA peak (2) the first order rate constant for the dehydration reaction. The results support a diffusion controlled mechanism for th:ldehydration with an energy and entropy of activations23 kJ mol-1 and -220 JK , respectively. INTRODUCTION In view of the wide application the effects
of thermal
dehydroxylation
treatment
and structure
Birch Holt et al investigated Mikhail pheres
et al studied
of clay minerals
on its properties
changes
became
of interest
the rate of thermal
the dehydration
in industry
especially
the study of
its dehydration,
in the past decade.
dehydration
of some clay minerals
of muscovite in various
(1).
atmos-
(2-4).
The present
study deals with the effect of exchangeable
DTA and the kinetics
of isothermal
dehydration
cations
of Jelsovy-Potok
on the TG,
montmorillonite.
EXPERIMENTAL The Jolsovy-Potok of different
exchangeable
Ca-Mg montmorillonite) cations, hours.
namely,
cations
derivatives
were prepared
by soaking 5g. of the original
in 100~~. of 0.1 N chloride
Li'+, Na', Cs+, Mg2+,
The prepared
solution
montmorillonite
derivative
and then with alcohol
and were kept under a relative
Ca2+,
was washed
sample
(usually
solution of the various
Sr2+ and Ba2' for a period of 12 five times with the specific
until the solution humidity
by replacement
chloride
was free from chloride
of 51.5-55%
in the temperature
ions
range
18-2O'C. Differential according
thermal
to the technique
Thermogravimetric an automatic
was carried out in a locally made apparatus
adopted by Mackenzie
analysis
thermobalance
0040-6031/85/$03.30
analysis
and kinetic
provided
(5) and McAdie
experiments
by Gebruder
0 Elsevier Science Publishers B.V.
Netzsch,
were
(6).
carried
out using
West Germany.
212 RESULTS
AND DISCUSSION
Thermogravimetric
and Differential
TG and DTA indicate ca 15O'C before
Thermal
that dehydration
dehydroxylation
region
more or less similar
derivatives,
(50-150°C),
attributed
whereas
of all the derivatives
hydration
is related
bonding
energy holding
derivatives tendency cation
studied
them inbetween
peaks are
(7-9).
water molecules
origin
The variation
the clay flakes.
The tendency
in
in the de-
liberated
to display more than one peak above 100°C, is attributed
of hydrated
at
show that they differ mainly
their dehydroxylation
to the amount of water molecules
and the of some to the
to form more than one shell surrounding
the
(8).
The effect of the charge density peak as a measure surface
of the potential
of the cation
ship was obtained difference Kinetics
energy binding
and the presence
surface on the highest DTA
the inner water
a satisfactory
shell to the
linear relation-
of two linear plots is related
to the
in the cation character.
of the Isothermal
DTA and TG results,
Dehydration
indicate
that the suitable
dehydration
isotherms
obeyed
constant,
k, are given in Table 1.
Mikhail
of the cation
is shown in Fig. 1, where
study of the isothermal
is between
first order kinetics
50'
temperature
range for the
and 150°C.
The dehydration
and the values
of the first order rate
First order kinetics
were also reported
by
et al (Z-4).
Table
1 shows that the k values,
for the divalent multivalent dehydration increases increase
cations
are higher
of the same cationic
cations
to tie clay mineral
process
(10).
the distance
an increase
Mg in vermiculite
contaminating
of separation
the dehydration
flakes
betweeen
than those
due to the tendency
together
to the tendency
reaction.
in the c dimension
and thus hindering as the cationic of large cations
the layers of montmorillonite
of the radius to and
This was proved by Walker who re-
from 14.4 to 15 A0 when Sr was replaced
by
(10).
The Ba derivative to the possibility
for the monovalent
radius,
It also shows that k increases
for the same series attributed
thus facilitating ported
to completion
at ca SOO'C.
to the use of the same clay mineral
the preparation peaks
takes place almost
starts and achieved
DTA of the seven montmorillonite in the dehydration
Analysis
is the only exception
of low temperature
the derivative
during
at low temperatures,
dehydroxylation its preparation.
probably
of Ba(OH)* which
due
could be
213
?tKfzx+ last
IlTA'penk
Catianic radius
(OC)
Fig.2 Variation cationic radius.
Fig.1 Variation of the last DTA peak with the charge density.
(A')
of k with the
TABLE 1. Values of the cationic radius, charge density and the first order rate-constant, for the various montmorillonite derivatives.
7o"c
85'C
100°C
120°c
140°c
Cationic* charge density (Cm-*I
Li
0.32
0.38
0.53
0.89
1.27
0.60
3.540
Na
0.41
0.64
0.91
0.65
1.80
0.95
1.410
CS
0.56
1.15
1.32
1.94
2.66
1.69
0.446
Mg
0.23
0.47
-
0.60
0.86
0.65
6.036
0.42
0.85
1.03
1.38
0.99
2.600
Ca Sr
0.34
0.70
0.96
1.22
1.53
1.13
1.990
Ba
0.33
0.42
1.02
-
1.67
1.35
1.400
A plot of k (s-l) at 14O'C against line for each group of derivatives, about the same gradient They differ
the cationic
The variation the cation, Table the variation flakes which
suggesting
in the electrostatic their distance and/or
the water molecules
adjacent
and third layers which The previous which
charge density
gave a straight lines are of to be operative.
due to the inhibition
of the reaction
rate constant with the charge density
to either
or both of the following
attraction
forces between
of separation
the change
= cationic
covalent bonds between
of mobile water molecules.
by considering
by the rate of desorption
of water molecules
through
charge/4Tr2.
the clay mineral
surface and those of the second
the fluidity
are confirmed
on
factors,
and hence the flow of water
in the partially
to the clay mineral
conclusions
by the rate of diffusion
Cationic
one and the same mechanism
in turn affects
is governed
radius,
two straight
charge.
1, is attributed
affects
The
Fig. 2.
of the dehydration
during dehydration,
hydration
the cationic
in the value of the intercept
upon increasing
*
Cationic radi s x 10'lo (In)
k x 10' (s-l)
Cationic derivative
the mechanism
of de-
from the surface followed
the lattice
interface.
If
214 the desorption changeable or probably obtained.
is rate determining,
to visualize
how the ex-
could affect the dehydration
rate and a value of the order of
higher
than the heat of evaporation
of water
Thus the diffusion
ed earlier,
it is difficult
cations
the exchangeable
reaction
cations affect the interlayer
water molecules
diffuse
micelle
Such a process would
edge.
(Z-4) would have been
is the rate determining,
from the hexagonal
since as mention-
spaces through which
holes in the sheet surface
involve an absorption
into the
of energy to push the
layers apart (12). A relatively high value of the energy of activation, Ea,ca -1 23kJmol , was obtained for all the derivatives studied attributed to a phenomenon known as "activated al diffusion", sional flow
was reported
energy of activation actions right
diffusion"
increase
in the value of Ea.
to yield two to three times higher values
than that of the three dimensional
(13), and is expected angles to the flakes.
the entropy
(2-4) or to what is known as "two dimension-
both lead to an apparent
of activation
to be due to a restricted
This is supported -1 ca 220 JK .
Two dimenof the free
due to the lateral translational
by a large negative
inter-
motion value
at
for
REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.
J. Birch Holt, I.B. Culter and M.E. Wadsworth, J. Am. Ceram. Sot., 41, (1958), 842. R.Sh. Mikhail, N.M. Guindy, and S. Hanafi, J. Appl. Chem., 20, (1970), 346. R.Sh. Mikhail and N.M. Guindy, J. Appl. Chem. Biotechnol. 21, (1971), 113. R.Sh. Mikhail, N.M. Guindy and S. Hanafi, Thermochimica Acta, 29, (1978), 289. R.C. Mackenzie, Differential Thermal Investigation of Clays, Mineralogical Section, London, 1957, reprinted 1966. H.G. McAdie, Anal. Chem., 39 (1967), 543. C.F. Walker and W.C. Cole, in "The Differential Investigation of Clays", Edited by R.C. Mackenzie, Mineralogical Society, London, 1957, 191 pp. G.T. Faust, Am. Miner, 36, (1951), 795. C.A. Alexinals, and M.I. Jackson 14th Nat. Conf. Clays and Clay Minerals, Berkeley, C.A., Pergamon Press, London 1966, 35 pp. G.F. Walker, Proc. Intern. Clay Conf., Stockholm, 1963, 177 pp. P.F. Low, in Clay Mineralogy, Edited by Grim, R.E. McGraw-Hill, 1968, 256 pp. R.C. Mackenzie and B.M. Bishui, Clay Minerals Bulletin, 3, (1957), 276. and Eyring in "The Theory of Rate Processes", Edited by S. W.J. Moore Glasstone, K.J. Laidler and H. Eyring, McGraw-Hill 1941, 512 pp.