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Zeolitization of pumice in ash-sodium salt solutions
Materials
Chemistry
ZEOLITIZATION
and Physics,
201-2
OF PUMICE IN ASH-SODIUM
L.M. SAIJA, R. OTTANA' Istituto
8 (1983)
di Chimica
SALT SOLUTIONS
and C. ZIPELLI
Industriale,
Via Salita S. Lucia
207
16
Facolta
di Scienze,
Universita
di Messina,
39, 98013 Pistunina-Messina
sopra Contesse,
(Italy)
N. BURRIESCI Istituto CNR di Ricerche ne e 1' Accumulo
sui Metodi e Processi
dell'Energia,
98013 Pistunina-Messina Received
pumice
The
media.
of zeolitization
39,
10 August 1982
has selectively
influence
per la Trasformazio-
sopra Contesse,
(Italy)
22 June 1982; accepted
ABSTRACT Lipari
Chimici
Via Salita S. Lucia
been
transformed
of NaOH concentration
into zeolites
and residence
in NaOH/NaCl
time on the degree
are discussed.
INTRODUCTION Natural
and
zeolites
synthetic
have
been
widely
in view of their useful physico-chemical
properties.
as
several
selective
the use
of
adsorbents zeolites
and
as additives
and additives
to fertilizers
and
of
low
cost
reported
to
both
alkaline
and
an
moreover
(pumice) have
made
arising the
be
and
be
a
series
from
have
by
successfully of
been
Formation high
reported
treatment
of
environment, by
To
conditions
to
into
disclose Lipari the
many Authors
in
by
simulate
under a the
which
product
of
for different
have
presence
these
been of
effects
rhyolitic
commercial
pumice.
effects
properties
nature
i.e.
reported
for animals
ion exchange
ratio
(7).
(1,6) have
feed supplement
zeolites
cation/OH-
transformed
experiments
alkaline
of
environment
preparative
hydrothermal of
a
saline
explore
Authors
to detergents,
industry
Beside their applications
in view of the efficient
material.
favoured
could
influence
solution
the
to
catalysts,
in
employed
zeolite
ash we
distribution
Besides alkaline natural
works and
on salt
materials
(7,8). 0254JJ584/83/0000~000/$03.00
0 Elsevier Sequoia/Printed
in The Netherlands
208
However, of glass
used
The
and
of zeolites
exploitation
made
all
dissolution
aggregates
are
though
of
(7).
under
chemical
process.
In
of
pumice) and products
fact,
this
combination
state
lack
on the formation
overcome
various
works
detailed
Fe
has
time,
been
times
several
of the zeolitization
in
for industrial
of
several
hydrothermal
temperature
examined
on kinetic
and crystalline
opportunities
residence
limitation
of
information
of large crystals
they also fail to disclose
the To
these
and NaOH
the
raw
weeks
runs
were
concentration.
material
(Lipari
process.
EXPERIMENTAL The
material
raw
was
rhyolitic
particle
size,
pumice
60
np,
from
Lipari
(PUMEX
commercial
Peerless),
mean
composition
(wt%): SiO2, 71.81; A1203, 12.74; Ti02, 0.14; Fe203, 1.75; FeO,0.64;
with
the
following
typical
K20, 3.63; Na20, 3.23; CaO, 1.36; MgO, 0.60; H20, 3.88; Total, 99.98 All of %
L
solid, NaOH
1 to The to
experiments =
All
10 hrs.
remove
of
liquid),
varying
products
out
were
of
XRD patterns containing
by comparing 100%
same
used
in
of
were
The
the
pumice
this
S/L
20
ratio
and
=
l/5,
conditions wt%
and
in a NaCl
dried
washed
product
residence
with
was
(S
(T =
saturated
(9). =
amount
95OC)
with
times
from
solution
(30%).
distillated
water
examined
X-ray
then
by
Cu Ku radiation.
various
zeolites
peak
zeolite under
paper,
a
to
run
the X-ray
certain
raw
9
filtered
chloride.
quantities
at
isothermal
from
(XRD) using Ni-filtered
Relative
the
carried
experiments
soluble
diffraction
those
amount
concentration
reaction
from
were
mean
intensities
species.
experimental
namely
were
higher
Such
estimated
with
those
samples
conditions
temperature
from
the
of samples
were
obtained
different
from
reaction
time
and
(10). Mdssbauer
spectra
in transmission indicated Water following
were
geometry
obtained
at
77
(LNT)
and
with a constant-acceleration
295
(RT) from
following
powders
the procedure
in ref. 11, 13. adsorption
capacities
the procedure
(at relative
previously
reported
humidity (12).
of 20%) were determined
209
RESULTS
AND DISCUSSION
Yields
of
(R-wt%) of starting 1
Fig. residence
shows time,
into zeolite, In
(conversion)
transformation
given
in
terms
of
%
residue
pumice.
the for
typical various
increases
kinetics % of NaOH.
with increasing
taking
particular,
are
into
account
of
transformation
as
a
function
The rate of transformation
of pumice
% of N&H. that
the
zeolitic
species
obtained
80
60
5c
‘1
‘3
‘5
‘7
‘9
I
Time(h) Fig. 1. % of residue, q NaOH = 12%; VNaOH
as a function = 15%;
l
of
of time. ARaOH
NaOH = 18%.
~9%;
ANaOH
= 11%;
210
are characterized
by a lower Si02/Al
2.3 wt% for Faujasite) tion
of
pumice
into
0 ratio (1.18 wt% for hydroxysodalite, 23 (5.5) and considering that the transforma-
than pumice zeolites
requires
solubility
is clear that high R values imply low conversion
of SiO as Na2SiO 2 3 and viceversa.
, it
25.
'1
3
5
‘7
Time
Ch)
Fig. 2. Degree of crystallization
l
NaQH
= 13%; ANaOH
Fig. time the
2
shows
at different induction
that
the
time
NaOH to
hydrothermal
and
amorphous
one
of
the
reactants
at
of
concentrations. decrease. process
increases
t = 7 hrs
of residence
as
Increasing
This
is
involves
easily
a
reaction
function
NaOH
of
by
interaction
a
higher
rate
and
causes
considering between
soda
concentration leads
to
a
of
higher
time.
in terms of the degree of crystallization as a function
= 9%;
residence
concentration
understood
chemical
consequently the
time.ONaOH
= 20%.
zeolitization
at equal residence
Product distribution measured
degree
alumina-silicate;
% of crystallization
as a function
= 16%; A NaOH
the
1
‘9
of % NaOH,
varies
(selectivity)
in the manner
shown
211
in
Fig.
indicating
3,
prevalence
of one
of
sodalite
(hereinafter
abundance
is strongly
three
the
main
following
indicated dependent
each
regions zeolites:
respectively
one
Zeolite
characterized Pc,Faujasite,
as PC, F and Hy) whose
by
the
Hydroxyrelative
upon the initial NaOH concentration.
: 10Q ._
p---b++--iL
z
N ._ 3
75_
‘9
‘11
’
‘13
’
, ‘15 Jr
’
‘20
% NaOH Fig. 3. Product
distribution
time of 7 hrs.
A
In fact, as shown of
PC
while
a
occurring
explained
by
the
solution.
with low Si02/A1203 Fig. function
4
shows
in Fig.
0
at
higher
the
of residence
favours
intermediate solubility
Therefore ratios
of NaOH concentraion
Faujasite;
l
at
the
favour the formation
Hydroxysodalite,
concentrations. of
SiO
2
higher
in
This
comparison
NaOH
time,
amount
of
at different
the
the
onset
of
trend
can
be
with
A1203
in
concentration
(like Hy) are the main products
relative
at residence
Zeolite PC.
3, low NaOH concentrations
concentration
high
Faujasite
alkaline
as a function
Hydroxysodalite;
zeolite
zeolites
formed.
species
NaOH concentration.
formed
as
a
At the highest
212
75 50_
,v”-*
25_
D----O--Q
0
Fig. 4, Zeolite species formed as a function of residence time, at different NaOH concentration. A Hydroxysodalite; 0 Faujasite; # Zeolite PC.
and lowest NaOH concentration there is no influence of residence time in the zeolite species formed. At any intermediateconcentration,an increase of residence time causes a
shift of the zeolite phases toward species
that are formed at lower NaOH concentration (Fig. 3). These considerations outline the difficulty of obtaining pure samples of any of the zeolitic species in the range of NaOH concentration from 9 to 13%.
213
Product
distribution
capacity
(12).
in
5
Fig.
maximum Fig.
as
a
exists
3,
Faujasite
In
fact,
of
function
of
behaviour species
at higher
is
which values
in the structure
Mossbauer
products
of of
the
of %
our
concentration.
It
of about
more
NaOH
of
water
allows
by
a
comparison
of
indicates
Fig. 5. Water adsorption tration.
than
noted
in
other
in the a higher
process.
capacity
zeolitic degree
species
the It
pumice
ratio
be
presence,
quantitative
distribution Fe2+/Fe
can
reported that
a
from above
this
zeolitic species
region, species.
is formed
large amounts of water due to the pore constraint
zeolitization
and
zeoli'ces is
the Hydroxysodalite
on the degree of crystallization
in
the H20 adsorption
11%. As evident
the
gain information
3+
through
on
result
adsorb
also
pumice, the
NaOH
adsorbed
of the Hydroxysodalite
spectroscopy
transformation
water
concentration
is not able to adsorb
implicit
the
amount
as a NaOH
this
of
which
The
can also be finger-printed
evaluation
chemical is
state
possible,
formed
zeolitization
on the zeolites
of of
in
the
Fe
in
fact,
to
the Fe 2i/Fe3+
by evaluating
structure of
(1).
(14). (14).
as a function
A lower Characte-
of NaOH concen-
214
rization of
several zeolite species obtained from pumice have revealed
very Small differences in the nature and distribution of iron which is 3+ to these results the raw pumice present only as Fe (14). In contrast shows large differences in the chemical state and distribution of iron 2+ J+ which is present both as Fe and Fe . The typical Mtissbauerspectra of the valcanic starting materials (Lipari pumice} and a zeolite {Hy) obtained by hydrothermal synthesis are shown in Fig. 6 and 7, respectively. These figures show that the variation on the Mossbauer spectra which 2+ accompany the zeolitization process only concern the Fe resonance line, which disappears when XRD gives evidence for a totally zeolitized product.
Fig. 6.
Iron-57 Mijssbauerspectrum measured at LNT of the Lipari Pumice.
215
l.OO_
c ii f0.99_
+ +
++ + l
+
5
a
-70 ‘8
‘6
‘4
-‘2.
Velocity Fig. 7. Typical
Iron-57 Mossbauer
pared by hydrothermal
synthesis
‘0
‘2
cmm-
spectrum
‘4
‘6
‘8
'10
s-9
measured
at LNT of the zeolites
pre-
from Lipari pumice.
CONCLUSION The
main
conditions
findings
of zeolites
Furthermore is
time - it
(
is
this
work
for the transformation
ly to a variety
- it
of
that
of pumice
the
variation
in alkaline
of
the
reactions
media leads selective-
such as Zeolite PC, Faujasite
and Hydroxysodalite.
is shown that:
possible
to
obtain
5 hr) acceptable difficult
expecially
are
to
the
zeolite
structure
from an industrial
obtain
pure
samples
by
using
a
residence
point of view; of
in the range of NaOH concentration
any
of
the
zeolitic
species
of 9 to 13% in our reaction
conditions.
ACKNOWLEDGEMENTS This are
work
has
indebted
for
the supervision
been
supported
financial
by
support.
Ente The
of Prof. Nicola Giordano
Minerario
research
has
Sicilian0 been
from the University
to
whom
conducted of Messina.
AA
under
216 REFERENCES 1.
D.W. BRECK - "The properties and applications of zeolites", Ed, R.P. Powsend, (London), 391 (1980).
2.
Y. MORI, Y. EDO, H. TORYO, IT0 - Zasso Kenky, 2,
21 (1974).
3.
I.M.J. SCHWUGER, H.G. SMOLKA - Colloid Polymer Sdi., 256, 270 (1978).
4.
K. TORI1 - in Proc. Conf. on Occurrence Properties and Utilization of Natural zeolites, Tucson, Arizona, June 6-14, 1976.
5.
S. VALENTE, S. CAVALLARO, N. BURRIESCI, S. GALVAGNO, C. ZIPELLI - Zeolites, in press.
6.
F. SCHWOCHOW, L. PUPPE - Angew. Chemie Internat. Edit., 14. 620 (1975).
7.
R. AIELLO, C. COLELLA, D.G. CASEY, L.B. SAND - Fifth Int. Conf. Zeolites, Naples, 1980, p. 49.
8.
H. HOTTA, K. TORII, M. ASAKA - "Synthesis of zeolite X from diatonite by the treatment with NaOH-NaC1 solution", Reports of the Government Industrial Research Institute, Tohoka, n0 6, November 1975, pp. 32-39.
9.
S.F. LUCA' - Unpublished
results.
10. L.M. SAIJA, R. OTTANA', C. ZIPELLI, N. BIJRRIESCI- Unpublished
results.
11. J.C.J. BART. N. BURRIESCI, F. CARIATI, G. MICERA, C. GESSA - Clays and Clay Minerals, s,
233 f1980).
12. R. OTTANA', L.M. SAIJA, N. BURRIESCI, N. GIORDAN~ - Zeolites, in press. 13. N. BURRIESCI ET ALTER - Bull. Sot. Min. Cris., 105, 43 (1982). 14. N. BURRIESCI, M. PETRERA, F. CARIATI, R. OTTANA', C. ZIPELLI - To be published.
Chemistry
ZEOLITIZATION
and Physics,
201-2
OF PUMICE IN ASH-SODIUM
L.M. SAIJA, R. OTTANA' Istituto
8 (1983)
di Chimica
SALT SOLUTIONS
and C. ZIPELLI
Industriale,
Via Salita S. Lucia
207
16
Facolta
di Scienze,
Universita
di Messina,
39, 98013 Pistunina-Messina
sopra Contesse,
(Italy)
N. BURRIESCI Istituto CNR di Ricerche ne e 1' Accumulo
sui Metodi e Processi
dell'Energia,
98013 Pistunina-Messina Received
pumice
The
media.
of zeolitization
39,
10 August 1982
has selectively
influence
per la Trasformazio-
sopra Contesse,
(Italy)
22 June 1982; accepted
ABSTRACT Lipari
Chimici
Via Salita S. Lucia
been
transformed
of NaOH concentration
into zeolites
and residence
in NaOH/NaCl
time on the degree
are discussed.
INTRODUCTION Natural
and
zeolites
synthetic
have
been
widely
in view of their useful physico-chemical
properties.
as
several
selective
the use
of
adsorbents zeolites
and
as additives
and additives
to fertilizers
and
of
low
cost
reported
to
both
alkaline
and
an
moreover
(pumice) have
made
arising the
be
and
be
a
series
from
have
by
successfully of
been
Formation high
reported
treatment
of
environment, by
To
conditions
to
into
disclose Lipari the
many Authors
in
by
simulate
under a the
which
product
of
for different
have
presence
these
been of
effects
rhyolitic
commercial
pumice.
effects
properties
nature
i.e.
reported
for animals
ion exchange
ratio
(7).
(1,6) have
feed supplement
zeolites
cation/OH-
transformed
experiments
alkaline
of
environment
preparative
hydrothermal of
a
saline
explore
Authors
to detergents,
industry
Beside their applications
in view of the efficient
material.
favoured
could
influence
solution
the
to
catalysts,
in
employed
zeolite
ash we
distribution
Besides alkaline natural
works and
on salt
materials
(7,8). 0254JJ584/83/0000~000/$03.00
0 Elsevier Sequoia/Printed
in The Netherlands
208
However, of glass
used
The
and
of zeolites
exploitation
made
all
dissolution
aggregates
are
though
of
(7).
under
chemical
process.
In
of
pumice) and products
fact,
this
combination
state
lack
on the formation
overcome
various
works
detailed
Fe
has
time,
been
times
several
of the zeolitization
in
for industrial
of
several
hydrothermal
temperature
examined
on kinetic
and crystalline
opportunities
residence
limitation
of
information
of large crystals
they also fail to disclose
the To
these
and NaOH
the
raw
weeks
runs
were
concentration.
material
(Lipari
process.
EXPERIMENTAL The
material
raw
was
rhyolitic
particle
size,
pumice
60
np,
from
Lipari
(PUMEX
commercial
Peerless),
mean
composition
(wt%): SiO2, 71.81; A1203, 12.74; Ti02, 0.14; Fe203, 1.75; FeO,0.64;
with
the
following
typical
K20, 3.63; Na20, 3.23; CaO, 1.36; MgO, 0.60; H20, 3.88; Total, 99.98 All of %
L
solid, NaOH
1 to The to
experiments =
All
10 hrs.
remove
of
liquid),
varying
products
out
were
of
XRD patterns containing
by comparing 100%
same
used
in
of
were
The
the
pumice
this
S/L
20
ratio
and
=
l/5,
conditions wt%
and
in a NaCl
dried
washed
product
residence
with
was
(S
(T =
saturated
(9). =
amount
95OC)
with
times
from
solution
(30%).
distillated
water
examined
X-ray
then
by
Cu Ku radiation.
various
zeolites
peak
zeolite under
paper,
a
to
run
the X-ray
certain
raw
9
filtered
chloride.
quantities
at
isothermal
from
(XRD) using Ni-filtered
Relative
the
carried
experiments
soluble
diffraction
those
amount
concentration
reaction
from
were
mean
intensities
species.
experimental
namely
were
higher
Such
estimated
with
those
samples
conditions
temperature
from
the
of samples
were
obtained
different
from
reaction
time
and
(10). Mdssbauer
spectra
in transmission indicated Water following
were
geometry
obtained
at
77
(LNT)
and
with a constant-acceleration
295
(RT) from
following
powders
the procedure
in ref. 11, 13. adsorption
capacities
the procedure
(at relative
previously
reported
humidity (12).
of 20%) were determined
209
RESULTS
AND DISCUSSION
Yields
of
(R-wt%) of starting 1
Fig. residence
shows time,
into zeolite, In
(conversion)
transformation
given
in
terms
of
%
residue
pumice.
the for
typical various
increases
kinetics % of NaOH.
with increasing
taking
particular,
are
into
account
of
transformation
as
a
function
The rate of transformation
of pumice
% of N&H. that
the
zeolitic
species
obtained
80
60
5c
‘1
‘3
‘5
‘7
‘9
I
Time(h) Fig. 1. % of residue, q NaOH = 12%; VNaOH
as a function = 15%;
l
of
of time. ARaOH
NaOH = 18%.
~9%;
ANaOH
= 11%;
210
are characterized
by a lower Si02/Al
2.3 wt% for Faujasite) tion
of
pumice
into
0 ratio (1.18 wt% for hydroxysodalite, 23 (5.5) and considering that the transforma-
than pumice zeolites
requires
solubility
is clear that high R values imply low conversion
of SiO as Na2SiO 2 3 and viceversa.
, it
25.
'1
3
5
‘7
Time
Ch)
Fig. 2. Degree of crystallization
l
NaQH
= 13%; ANaOH
Fig. time the
2
shows
at different induction
that
the
time
NaOH to
hydrothermal
and
amorphous
one
of
the
reactants
at
of
concentrations. decrease. process
increases
t = 7 hrs
of residence
as
Increasing
This
is
involves
easily
a
reaction
function
NaOH
of
by
interaction
a
higher
rate
and
causes
considering between
soda
concentration leads
to
a
of
higher
time.
in terms of the degree of crystallization as a function
= 9%;
residence
concentration
understood
chemical
consequently the
time.ONaOH
= 20%.
zeolitization
at equal residence
Product distribution measured
degree
alumina-silicate;
% of crystallization
as a function
= 16%; A NaOH
the
1
‘9
of % NaOH,
varies
(selectivity)
in the manner
shown
211
in
Fig.
indicating
3,
prevalence
of one
of
sodalite
(hereinafter
abundance
is strongly
three
the
main
following
indicated dependent
each
regions zeolites:
respectively
one
Zeolite
characterized Pc,Faujasite,
as PC, F and Hy) whose
by
the
Hydroxyrelative
upon the initial NaOH concentration.
: 10Q ._
p---b++--iL
z
N ._ 3
75_
‘9
‘11
’
‘13
’
, ‘15 Jr
’
‘20
% NaOH Fig. 3. Product
distribution
time of 7 hrs.
A
In fact, as shown of
PC
while
a
occurring
explained
by
the
solution.
with low Si02/A1203 Fig. function
4
shows
in Fig.
0
at
higher
the
of residence
favours
intermediate solubility
Therefore ratios
of NaOH concentraion
Faujasite;
l
at
the
favour the formation
Hydroxysodalite,
concentrations. of
SiO
2
higher
in
This
comparison
NaOH
time,
amount
of
at different
the
the
onset
of
trend
can
be
with
A1203
in
concentration
(like Hy) are the main products
relative
at residence
Zeolite PC.
3, low NaOH concentrations
concentration
high
Faujasite
alkaline
as a function
Hydroxysodalite;
zeolite
zeolites
formed.
species
NaOH concentration.
formed
as
a
At the highest
212
75 50_
,v”-*
25_
D----O--Q
0
Fig. 4, Zeolite species formed as a function of residence time, at different NaOH concentration. A Hydroxysodalite; 0 Faujasite; # Zeolite PC.
and lowest NaOH concentration there is no influence of residence time in the zeolite species formed. At any intermediateconcentration,an increase of residence time causes a
shift of the zeolite phases toward species
that are formed at lower NaOH concentration (Fig. 3). These considerations outline the difficulty of obtaining pure samples of any of the zeolitic species in the range of NaOH concentration from 9 to 13%.
213
Product
distribution
capacity
(12).
in
5
Fig.
maximum Fig.
as
a
exists
3,
Faujasite
In
fact,
of
function
of
behaviour species
at higher
is
which values
in the structure
Mossbauer
products
of of
the
of %
our
concentration.
It
of about
more
NaOH
of
water
allows
by
a
comparison
of
indicates
Fig. 5. Water adsorption tration.
than
noted
in
other
in the a higher
process.
capacity
zeolitic degree
species
the It
pumice
ratio
be
presence,
quantitative
distribution Fe2+/Fe
can
reported that
a
from above
this
zeolitic species
region, species.
is formed
large amounts of water due to the pore constraint
zeolitization
and
zeoli'ces is
the Hydroxysodalite
on the degree of crystallization
in
the H20 adsorption
11%. As evident
the
gain information
3+
through
on
result
adsorb
also
pumice, the
NaOH
adsorbed
of the Hydroxysodalite
spectroscopy
transformation
water
concentration
is not able to adsorb
implicit
the
amount
as a NaOH
this
of
which
The
can also be finger-printed
evaluation
chemical is
state
possible,
formed
zeolitization
on the zeolites
of of
in
the
Fe
in
fact,
to
the Fe 2i/Fe3+
by evaluating
structure of
(1).
(14). (14).
as a function
A lower Characte-
of NaOH concen-
214
rization of
several zeolite species obtained from pumice have revealed
very Small differences in the nature and distribution of iron which is 3+ to these results the raw pumice present only as Fe (14). In contrast shows large differences in the chemical state and distribution of iron 2+ J+ which is present both as Fe and Fe . The typical Mtissbauerspectra of the valcanic starting materials (Lipari pumice} and a zeolite {Hy) obtained by hydrothermal synthesis are shown in Fig. 6 and 7, respectively. These figures show that the variation on the Mossbauer spectra which 2+ accompany the zeolitization process only concern the Fe resonance line, which disappears when XRD gives evidence for a totally zeolitized product.
Fig. 6.
Iron-57 Mijssbauerspectrum measured at LNT of the Lipari Pumice.
215
l.OO_
c ii f0.99_
+ +
++ + l
+
5
a
-70 ‘8
‘6
‘4
-‘2.
Velocity Fig. 7. Typical
Iron-57 Mossbauer
pared by hydrothermal
synthesis
‘0
‘2
cmm-
spectrum
‘4
‘6
‘8
'10
s-9
measured
at LNT of the zeolites
pre-
from Lipari pumice.
CONCLUSION The
main
conditions
findings
of zeolites
Furthermore is
time - it
(
is
this
work
for the transformation
ly to a variety
- it
of
that
of pumice
the
variation
in alkaline
of
the
reactions
media leads selective-
such as Zeolite PC, Faujasite
and Hydroxysodalite.
is shown that:
possible
to
obtain
5 hr) acceptable difficult
expecially
are
to
the
zeolite
structure
from an industrial
obtain
pure
samples
by
using
a
residence
point of view; of
in the range of NaOH concentration
any
of
the
zeolitic
species
of 9 to 13% in our reaction
conditions.
ACKNOWLEDGEMENTS This are
work
has
indebted
for
the supervision
been
supported
financial
by
support.
Ente The
of Prof. Nicola Giordano
Minerario
research
has
Sicilian0 been
from the University
to
whom
conducted of Messina.
AA
under
216 REFERENCES 1.
D.W. BRECK - "The properties and applications of zeolites", Ed, R.P. Powsend, (London), 391 (1980).
2.
Y. MORI, Y. EDO, H. TORYO, IT0 - Zasso Kenky, 2,
21 (1974).
3.
I.M.J. SCHWUGER, H.G. SMOLKA - Colloid Polymer Sdi., 256, 270 (1978).
4.
K. TORI1 - in Proc. Conf. on Occurrence Properties and Utilization of Natural zeolites, Tucson, Arizona, June 6-14, 1976.
5.
S. VALENTE, S. CAVALLARO, N. BURRIESCI, S. GALVAGNO, C. ZIPELLI - Zeolites, in press.
6.
F. SCHWOCHOW, L. PUPPE - Angew. Chemie Internat. Edit., 14. 620 (1975).
7.
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8.
H. HOTTA, K. TORII, M. ASAKA - "Synthesis of zeolite X from diatonite by the treatment with NaOH-NaC1 solution", Reports of the Government Industrial Research Institute, Tohoka, n0 6, November 1975, pp. 32-39.
9.
S.F. LUCA' - Unpublished
results.
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233 f1980).
12. R. OTTANA', L.M. SAIJA, N. BURRIESCI, N. GIORDAN~ - Zeolites, in press. 13. N. BURRIESCI ET ALTER - Bull. Sot. Min. Cris., 105, 43 (1982). 14. N. BURRIESCI, M. PETRERA, F. CARIATI, R. OTTANA', C. ZIPELLI - To be published.